Fiio K9 Pro ESS review: An outstanding high-end desktop DAC/amp

Fiio is a brand that needs no introduction; the Chinese audio manufacturer is well-known for its budget DACs and IEMs, and over the last 18 months it has branched out into new product categories and set its sights on the mid-tier and high-end segments. The result is the K9 Pro, a flagship desktop DAC/amp that delivers an incredible set of features. It has dual ESS ES9038PRO DACs, a 6.35mm port alongside balanced 4-pin XLR and 4.4mm ports, MQA and DSD decoding, Bluetooth 5.1 connectivity with high-res wireless codecs, and a custom stand that lets you mount the unit vertically.

In short, you're getting all the features you could ask for in a high-end DAC/amp, and that's a good thing considering the K9 Pro costs $849. For context, that's nearly six times costlier than the K5 Pro. The K9 Pro has much better internals — the DACs in use are the same as the M17 music player, and that retails for $1,700 — and you get an elegant design that looks great on your desk. Furthermore, the sheer number of features on offer make it a great option as an end-game DAC.

I've used the Fiio K9 Pro for over three months now, and here's why I think this is the ultimate all-in-one choice if you want a high-end DAC/amp for use with headphones.

Fiio K9 Pro ESS: Pricing and availability

Fiio unveiled the K9 Pro in Q4 2021, with the first iteration of the product coming with AKM DACs. But given the shortage of the same, Fiio pivoted to ESS, relaunching the K9 Pro at the start of 2022 with the ESS ES9038PRO instead. The AKM version was initially available for $699, but you can't get your hands on that model and will need to go with the ESS variant if you're eyeing this DAC.

The ESS version of the K9 Pro costs $849 on Amazon and Fiio's website, and you can get your hands on the DAC at major audio retailers globally. As is the case with other Fiio DACs, you get a standard two-year warranty.

Fiio K9 Pro ESS: Design

Fiio isn't known for its flashy designs, with the brand instead delivering products with a clean aesthetic that looks good on your desk. That's what you get with the K9 Pro as well; the design doesn't stand out too much, but it is immediately evident that this is a high-end product. There's a Pro label prominently visible to the left, and the large volume knob decked out in gold and an RGB LED ring encircling it give K9 Pro a little more panache on the styling front.

The black anodized aluminum design makes the DAC look that much more elegant, and while the overall design is more rectangular than the K5 Pro, the beveled edges at the front make the unit feel less boxy. With dimensions of 200 x 224.5 x 72mm and a weight of 6lb (2.7kg), the K9 Pro has a reassuring heft to it. There are vents on either side of the unit for managing heat, and they do a decent enough job ensuring the K9 Pro doesn't get too hot.

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Coming to the connectors, you'll find a single-ended 6.35mm port at the front along with a 4-pin balanced XLR port and a 4.4mm balanced port. To the right of the front panel, you'll find status indicators that highlight the connection mode that's currently active. There are four buttons to the bottom of the right that let you power the unit on or off, changing the gain levels, switch sources, and select what configuration to use the K9 Pro in: a DAC, preamp, or DAC/amp.

At the back, you'll find an exhaustive list of inputs that include both digital and analog. On the digital front, you get USB, Bluetooth, coaxial, and optical. As for analog, there's RCA and 4.4mm line in as well as RCA out and a balanced 3-pin XLR out. Fiio hasn't left anything out here, and you also get a USB-C port on the right side of the unit that makes it straightforward to connect a mobile source.

The build quality itself is phenomenal, and there are zero issues in this area. The clean lines combined with the metal chassis make the K9 Pro look unmistakably premium, and you get all the connectivity options you want. My only quibble in this area is that the labels for the buttons at the front aren't visible against the design, and I had to use the flashlight on my phone for making any changes. While the design has a matte finish, the volume knob has a glossy coat and picks up smudges fairly easily. Other than that, it has been smooth sailing with the K9 Pro.

Fiio K9 Pro ESS: Features

Fiio bundles the K9 Pro in a large box that contains the DAC along with a host of accessories. You get rubber feet, USB-A to USB-B cable, 3.5mm to 6.35mm connector, a custom stand that lets you mount the unit vertically — to free up room on your desk — and a Bluetooth antenna that affixes at the back. 

The first thing you do after unboxing the K9 Pro is select the voltage; there's a switch located on the underside of the unit that lets you change between 115V and 230V, and you need to set it accordingly for your region. I'm using the DAC in India, and the unit was set to 230V out of the box, so I didn't see any need to change it.

Coming to the audio hardware, the K9 Pro features flagship-tier ESS Sabre Pro ES9038PRO DACs, and they're used in a dual-channel configuration. There are two THX AAA 788+ linear amplifiers that have been customized for the K9 Pro, the standard 788 module was prone to overheating with continuous use, so Fiio worked with THX over the 788+ to deliver better heat dissipation and more output power.

On the wireless front, you get Qualcomm's QCC5124 audio SoC that enables Bluetooth 5.0 and comes with a host of wireless codecs, including AptX HD, AptX LL, and LDAC. Switching to wireless mode is effortlessly easy, and I didn't have any issues connecting to the DAC via the best Android phones. Thanks to the antenna boosting the range, I had zero issues with connectivity or range, with the DAC staying connected to my Pixel 7 Pro over 30 feet away.

You get the full 384kHz/32-bit PCM and DSD256 decoding when connecting the K9 Pro via USB to your host device, and it goes down to 192kHz/24-bit over coaxial and 96kHz/24-bit with optical. There's 8x MQA decoding as well, and it's safe to say that Fiio didn't leave anything out on the connectivity side of things.

You don't get a screen here, but like the K5 Pro, the RGB LED ring encircling the volume knob changes color based on the sampling rate. As there's wireless connectivity here, you get a visual indicator of the audio codec in use when streaming over Bluetooth. For wired mode, blue is highlighted for playback under 48kHz, switching to yellow for over 48kHz, green for DSD files, and violet for MQA playback. With wireless, the color switches to blue for SBC, cyan for AAC, yellow for AptX HD, violet when using AptX/AptX LL, and white with LDAC.

You can tweak settings by using the Fiio Control app, including adjusting the brightness of the LED light around the volume knob (or turning it off entirely), choosing the Bluetooth codec, adjust the channel balance, and customize the EQ. You get a few presets as well as a 10-band EQ if you want granular control. There's also a built-in guide that walks you through the various ports and features of the K9 Pro, a handy addition if you're just getting started with the DAC.

Fiio K9 Pro ESS: Sound quality

The K9 Pro delivers 2.1W of power at 32ohm and 1.1W at 300ohm over the balanced 4.4mm and XLR ports, with an SNR of 123dB. For the single-ended 6.35mm port, you get 2.1W of power at 32ohm and 281mW at 300ohm, with an SNR of 129dB. Basically, the K9 Pro has more than adequate power for driving just about anything, from sensitive IEMs to headphones with a high impedance. You get three gain levels to choose as well — low, medium, and high — with each mode seeing a 6dB increment.

There is no background hiss whatsoever, and the K9 Pro is ideally suited for use with headphones. The defining characteristic of this DAC is its clean and transparent sound, with Fiio absolutely nailing the brief in this area. You get excellent tonality and dynamic range here, and the DAC does a brilliant job getting out of the way and allowing headphones and IEMs to shine.

I used the K9 Pro predominantly with the Focal Elex — connected via balanced XLR — and this pairing worked incredibly well. The K9 Pro unlocked the full potential of the Elex, delivering bass that's full of vigor and energy, dynamic mids, and detailed highs. I also used it with the Audeze Euclid and Fiio's own FA7S IEMs, and in each situation, the DAC delivered a clean and balanced sound that was wonderful. 

The low-end detail is outstanding, with plenty of character and detail retrieval, and that is immediately evident with IEMs as well as headphones. There's good presence in the sub-bass frequencies, you get a good overall texture here, and the mid-bass is controlled well. The mids and clean and detailed, with realistic instrument timbre that makes the K9 Pro shine, and you get excellent detail retrieval with great tonality for vocals. The treble lends a lot of airiness to the sound, with good extension and clarity.

The stereo imaging is exquisite, with the K9 Pro delivering a well-rounded sound that's very enjoyable. Fiio has nailed the technical brief with the K9 Pro, and the DAC is among the best in the sub-$100 category. If you're using a budget DAC and are looking to upgrade, you will see a difference with the K9 Pro — the DAC unlocked nuances in songs that I hadn't noticed before while using the same IEMs. 

Fiio K9 Pro ESS: The competition

If you're in the market for an integrated DAC/amp that has extensive connectivity options, you should consider Matrix Audio's Mini-i Pro 3. The DAC has 3.5mm and a balanced 4.4mm port at the front, all the digital and analog connectivity options you want at the back, and it has Bluetooth in addition to Wi-Fi. There's also a full-color screen at the front with a clean UI, and you get DSD512 along with MQA decoding. The Mini-i Pro 3 is costlier at $1,025, but you are getting a bit more on the feature side of things.

The RME ADI-2 is another alternatives that ticks all the right boxes. It costs a lot at $1,299, bit you get balanced 4.4mm and a standard 3.5mm port at the front, RCA and balanced out, DSD512 and MQA decoding, and a screen at the front that shows connection information. It misses out on Bluetooth, but if that isn't a consideration, there is a lot to like here.

Fiio K9 Pro ESS: Should you buy it?

You should buy this if:

• You want an all-in-one desktop DAC/amp
• You want wireless connectivity and high-res AptX codecs
• You're looking for extensive wired connectivity options
• You want a high-end DAC with an exquisite sound signature
• You need MQA and DSD256 decoding

You shouldn't buy this if:

• You want a DAC with a built-in screen or remote control
• You absolutely need 16x MQA and DSD512 decoding

Fiio may not be known for its prowess in the high-end category, but the Chinese brand did a fantastic job with the K9 Pro. The clean lines along with the elegant design make the unit look premium, and while you don't get a screen here, it's easy enough to change modes via the buttons located at the front. The RGB LED ring makes a big difference in highlighting what mode is currently active, and the build quality is fantastic.

There isn't anything missing on the connectivity front, with the balanced 4.4mm and XLR ports along with the 6.35mm port covering all the options for headphones use. The digital and analog connections at the back allow the K9 Pro to be used as a standalone DAC or just a preamp, and the best part here is the Bluetooth connectivity. It makes the DAC that much more versatile, and unlocks a new dimension to Fiio's desktop portfolio.

The sound signature is transparent, allowing the DAC to fade away into the background and letting your headphones shine. Fiio has nailed the technical presentation here, and I don't see myself switching to another DAC in the foreseeable future. If you want a high-end desktop DAC/amp combo that delivers an analytical sound, the Fiio K9 Pro is a fantastic choice.