FiiO K9 Pro ESS Review

FiiO K9 Pro ESS

In this article, we review the FiiO’s Flagship All-in-One device, the K9 Pro ESS. It costs $849 USD from FiiO, directly.


Disclaimer: FiiO sent us the K9 Pro ESS for this review, free of charge. I only covered the customs fees & taxes. All thoughts and experiences with the product are naturally my own.


FiiO is one of the most popular audiophile-focused companies in the world. They design and manufacture a wide variety of audio products for different price brackets. They have been in this industry since 2007 and they are very popular with fans all around the world. Today, we are looking at their new K9 Pro ESS flagship desktop DAC & AMP. We have reviewed and awarded a lot of FiiO gear here on Headfonia over the years and you can read those reviews here: Headfonia FiiO Reviews.

FiiO K9 Pro ESS Desktop DAC/AMP/PRE with Bluetooth

The K9 Pro ESS’s dedicated web page can be found here.  It costs $849 USD from FiiO’s official Aliexpress Store.  You can also find the up-to-date Windows drivers here. Take a look at the highlights & specs list of the K9 Pro ESS, then we dive into the details, together.

  • x2 ESS Technology ES9038PRO Flagship DACs
  • Toroidal Linear Power Supply + Nichicon Caps
  • THX AAA 788+ Amp Module (≈2.1W @32Ω)
  • Fully Balanced Architecture with x8 OPA1612
  • Dual Femto-Second Crystal Clocks, LDOs & More.
  • Isolated Digital & Analog Power
  • Bluetooth 5 + LDAC 24bit/96kHz, APTX/HD, SBC, AAC
  • XMOS XU-208 USB Controller
  • 32bit 384kHz PCM & DSD256 + MQA x8 Support
  • Upgradeable Firmware

The Fiio K9 Pro ESS is FiiO’s take on the ultimate, all-in-one desktop system. It has a killer circuitry, along with a rigid and well-designed chassis. It offers plenty of ports, suitable for every-use scenario. I’ve been using K9 Pro for about 2 months. In my 10-year audiophile journey, only a few products have excited me as much as this device, and I will explain why, in detail. We have reviewed many DACs and AMPs over the last 2 years on Headfonia. As a result of the rapid increase in component quality and the relentless efforts of various companies, we can now get high-end DAC and amps that were worth a small fortune a few years ago, at a much more affordable price.

FiiO K9 Pro ESS

Throughout these few paragraphs, I will give you various information about the K9 series. FiiO’s K9 series consists of two products for now. The K9 Pro AKM and K9 Pro ESS. The K9 Pro AKM version uses AKM’s AK4499 flagship DAC chip. The ESS version uses 2 of ESS Technology’s flagship ES9038PRO DAC chips. You may have noticed that the K9 Pro AKM uses a single chip. In October 2020, an unfortunate fire broke out at the Asahi Kasei Microdevices (AKM) factory in Mizayaki, Nobeoka, which created a shortage of AKM chips. Companies had to make changes to many of the devices they designed before the fire to deal with the short supply. The original K9 Pro AKM was meant to use dual 4499s, instead of a single one but it was impossible to procure chips so this design change was out of necessity, rather than an optional one. FiiO states that the K9 Pro AKM is a limited-run product and it is unknown when the AKM chips will be in stock.

Hence, they started designing the ES9038PRO version. FiiO states that they understand replacing a DAC chip in a design sounds simple enough, but it’s actually a rigorous debugging and verification process. They state that they need to complete a thorough quality index test, reliability test, and environmental test before introducing the unit to mass production. They also state that these tests take 2 to 3 months, maybe more, depending on the complexity of the PCB. They also state that they did everything they could do to reduce the impact of the supply shortages on the customers, both time & cost-wise. We’ll talk about this and more in the upcoming section. 

FiiO K9 Pro ESS

Packaging & Accessories

I think you are all familiar with the packaging design that FiiO has been using since 2021. The outer surface of the package is covered with a coating that gives a kind of rainbow effect and in my opinion, this package looks much more appealing than the previous packaging, which was plain and ordinary. We are happy that they continued with this futuristic design, as they won the appreciation of not only us but also many audiophiles around the world. 

The K9 Pro ESS comes in a pretty big box. On the front side of the box, there is an illustration featuring the outline of the device. FiiO did not list any details or specs about the device anywhere on the box. The first thing we see when we open the box is a WARNING brochure. It states that the product contains a linear power supply and you are asked to set your local nominal voltage manually via the switch on the back of the product. I suggest paying attention here, choosing the wrong voltage type may result in damage to the device and none of us want that. 

When we remove the foam that protects the top of the device, we see a large accessory box on the side. Apart from that, we also get our first real idea of the size of the device. Considering that it is an all-in-one device that offers top-tier performance, I would like to say that the size of the K9 Pro ESS, is ideal. As for accessories, the K9 Pro ESS comes with a power cable, a replacement fuse, a USB-A to USB-B cable, a Bluetooth antenna, six pieces of adhesive rubber feet, a vertical stand, and a 6.35mm headphone adapter, lastly, a user’s manual booklet. My favorite accessory is by far the vertical stand. It is nice of FiiO to include such a useful tool. The device looks really good standing up and that way, it can work as a headphone holder as well! I expect to see this accessory with every DAC & AMP combo out there. It’s great for saving space on a crowded desk.

FiiO K9 Pro ESS

Design & Build Quality

Top-notch. Measuring 20 x 22 x 7 centimeters, the K9 Pro ESS is not a particularly small device. However, since it is a higher-end, all-in-one device that comes with a vertical stand, I think the size is not going to be an issue here. Plus, if you take a look at the FiiO’s PCB, you’ll see that the FiiO engineers have filled every bit of the available space on the device. If this PCB had a codename, FiiO would call it “overkill”. 

The design elements of the aluminum case are reminiscent of FiiO’s current line of digital audio players, but with more elegant, softer design cues. The precision-milled aluminum case with a sandblasted matte black finish is a dangerous combination and could win any enthusiast’s heart. I really liked the design. The size is convenient, and the device has wonderful build quality. I expected no less from a higher-end unit from FiiO and I was not disappointed, at all. The K9 Pro ESS looks and feels rigid, durable, and well-built. Small details like the LED placement under the volume knob, the radiant design buttons, and gold detailings enhance the premium feel.

The device layout is quite simple and neat. FiiO has designed a device that looks both stylish and professional. On the front panel, there are the device’s controls, 3.5mm, 4.4mm, XLR 4-pin headphone outs, volume knob, and status LEDs. The device does not come with a remote controller, but thanks to the cleverly designed front panel, it is quite easy to control the device. Additionally, the FiiO Control app that is available both on Android and iPhones helps control the device from afar. More on that later.

Like most DAC & AMP devices, the main I/O options are located on the back of the device. The K9 Pro ESS offers many different ports for many different usage scenarios. From left to right, we see an IEC C13 power socket, Bluetooth antenna socket, USB-B input, coaxial input, optical input, 4.4mm input, unbalanced RCA inputs, and outputs. The K9 Pro ESS also offers balanced XLR outputs on the far right of the back panel. The I/O options are quite rich and the inclusion of 4.4mm input is rare, especially below the thousand dollars mark. FiiO did their best to squeeze in as many options as they can into the chassis of their flagship DAC & AMP. The RCAs and the XLR sockets are gold-plated and every I/O on the device feels rigid and high quality. I can’t see any imperfections, milling defects, or assembly issues anywhere on the chassis. We covered every port on the device, except for one. There is a USB-C port located on the right panel of the device. FiiO states that it can be used with OTG devices, so you can directly use your phone or DAP as a streamer.

In addition, unlike the K9 Pro AKM, the ESS version comes with ventilation holes around the chassis. These vents are vital for cooling the Dual ES9038 DACs and the THX amp module, which generate a lot more heat than AKM’s 4499 DAC. Apart from that, looking at the volume pot is sufficient to distinguish the two products from each other in terms of design. While the ESS version is equipped with a golden volume pot, the AKM version comes with a black volume pot decorated with a chrome outline. Overall, I can say that the K9 Pro ESS satisfied me both in terms of design, build quality, and component selection. It’s a job well done by FiiO. 


The review continues on Page Two, after the click HERE or by using the jump below.

Page 2: Technology & Audio Circuitry, Controls & Operation

Page 3: DAC Performance, DAC-AMP Performance, Low, Mid, High

Page 4: Power, Technical Capability, Comparisons, Conclusion

4.4/5 - (296 votes)

Long time Tech Enthusiast, an ambitious petrol-head, Yagiz likes his gadgets and always finds new ways into the tinkerer's world. He tries to improve anything and everything he gets his hands onto. Loves an occasional shine on the rocks.


  • Reply April 17, 2022

    James McCook

    Great review thanks.
    Good to know that FiiO is stepping up

  • Reply April 24, 2022

    Israel Silverman

    How does it compare against the AK4499 version?

    • Reply February 2, 2023

      Wojciech Szymański

      which headphone output is the best?

      • Reply February 7, 2023


        The BAL 4.4mm and XLR 4-pin are the same. They perform superior compared to the UNBAL 3.5mm HPO.

  • Reply July 23, 2022


    What are your thoughts when you compare the Shanling EM5 against the Fiio K9 pro ess. they are both the same price and i know you have done a review of both.

    • Reply July 25, 2022


      I did not review the EM5 therefore I don’t know.

      • Reply February 10, 2023

        Hans P. Heilmann

        How is Audeze mm50 to listen with Fiio K9 Pro ESS ?

        Thank you for a goid review.

  • Reply February 13, 2023


    Comparison with 400$ range products? i think this dac-amp should be compared with adi-2pro or Dac 3 of benchmark.

  • Reply May 6, 2023

    Fernando Machado

    Hello from Brazil! I’m new to the party, looking for a DAC/headphone amp. Here I found a old Corda Symphony selling for about USD660 and I would like to know how it compares to the new FiiOs! Regards!

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