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FiiO K9 Pro ESS
Desktop DAC and Amplifier
High performance DAC ES9038PRO*2 | THX AAA 788+ Tech | App control
Dual femtosecond clocks | QCC5124 Bluetooth chip | Truly balanced design
Supports LDAC/aptX Adaptive/aptX HD | Dual voltage linear transformer
Wide connector selection
*Pictures are for reference only. The actual product may vary.
* Due to the instability of the supply chain, some materials may be replaced due to shortage. The accompanying drawings are for reference only.
Moves your human “core”,
and not just by a little!
Inside the K9 Pro ESS are 2 ES9038PRO DAC chips, specifically designed for maximum performance in desktop-grade equipment. One ES9038PRO chip, with all of its 8 parallel outputs, is used for each channel to achieve richly detailed sound with minimal distortion.
Pure clean sound,
satisfying even demanding listeners
The THX AAA 788+ chips used in the K9 Pro ESS provide exemplary details and dynamics no matter if you are using low or high-impedance headphones. The K9 Pro ESS can produce an undistorted 1100mW* under a 300Ω load, and an undistorted 2100mW* under a 32Ω load, 50% higher than the original THX AAA 788 amplifier chips.
*As tested in FiiO Labs under balanced out.
Precise Design
Six-stage audio circuit, to reveal every last detail
Fully differential, fully balanced design
Every audio signal goes through a mammoth 6-stage circuit to reproduce music as faithfully and as detailed as possible.
Fully differential signals go through the DAC, volume adjustment, and amp for a truly balanced design. Such a design ensures minimal interference between different components in order to fully maintain all details and large dynamic swings in music for unmatched sound quality.
Separated analog and digital sections,
partitioned design
The PCB of the K9 Pro ESS uses a partitioned layout, wherein not only the power supply and signals are separated, but the analog signal loop is also put in an independent section, guaranteeing the integrity of the audio signal being processed.
Electricity is the mother of sound
Just pure sound,
Isolated digital and analog power delivery
Quality and quantity,
LDOs for each circuit stage
The digital portions of the K9 Pro ESS physically receive power separately from the analog portions, for effective shielding against audio interference between the two circuits. This ensures pure and faithful reproduction of your music.
Immensely robust,
Linear power supply
Besides the special high-performance linear power supply, the power stabilization and filtering within the audio circuit is also a big contributor to the K9 Pro ESS’s excellent sound. Specifically, in each stage of the audio circuit, ultra-low-noise LDOs are employed for voltage regulation.
Electricity is the mother of sound, so special attention was paid to optimizing the K9 Pro ESS’s power supply to ensure excellent sound. The K9 Pro ESS’s linear power supply, with its low-frequency transformer and 4 massive 4700uF capacitors, makes sure that the rest of the system gets abundant clean power.
Dual femtosecond clocks，Precise clock management
A dual-mode clock management design is utilized for the K9 Pro ESS. Under USB and Bluetooth decoding, dual asynchronous femtosecond clocks are used, while under optical and coaxial decoding, automatic PLL clocks are employed. A more precise clock management system makes it easier to handle any kind of source and maintain the maximum quality possible.
MQA Renderer, Lossless sound reproduction
The K9 Pro ESS supports the unfolding of MQA tracks, allowing you to listen to high-resolution audio files that are not only reasonably sized, but also retain master-level sound quality that bring you directly into the recording studio.
*With an appropriate music player supporting MQA, the K9 Pro ESS supports up to 8x unfolding
Fast and reliable
Hi-Res Bluetooth
The K9 Pro ESS employs the Qualcomm QCC5124 to handle Bluetooth duties, with support for formats such as LDAC, aptX HD and aptX Adaptive. This chip ensures that Bluetooth connections are both reliable and quick, satisfying both the low latency needs for games/videos and the high bitrate necessary for high-resolution audio. * Bluetooth format support: AAC/SBC/aptX/aptX LL/aptX HD/LDAC/aptx Adaptive
Essentiality of volume adjustment
Adjusting the volume may look like a simple concept, but a good execution of it is crucial to an excellent audio experience. The ADC curve reconstruction method of volume adjustment used in the K9 Pro ESS effectively minimizes any left-right channel volume imbalance and noise. It also results in a smooth change of volume across all levels. This attention paid to the simple process of volume adjustment is just another layer to making sure you truly savor your music with the K9 Pro ESS.
Lighting up the mood
The RGB indicator lights surrounding the volume knob can light up differently depending on the currently playing sampling rate.
Dial it in with
three gain levels
Choose between high, medium, and low gain with a physical switch to fit exactly your needs when listening to your particular pair of headphones. Thanks to the pure hardware gain circuit, even when listening at low gain with high-sensitivity headphones both dynamic range and musical fidelity remain uncompromised.
Plentiful connectors to choose from
Front: XLR 4-pin, 4.4mm balanced, 6.35mm single-ended headphone outputs
XLR-4
4.4mm balance
6.35mm single end
Rear: 4.4mm balanced line in; coaxial, optical, Bluetooth, RCA, USB input; RCA SE out and XLR*2 balanced out
XLR balanced output
Coaxial
RCA
Optical
Side：USB Type-C port
Type C port
Professional PEQ For what you love
Through the FiiO Control app, you can quickly switch between 7 music tuning styles preset on the K9 Pro ESS. If the selected tuning style fits the music you are listening to, you can acquire a more vivid and pleasant experience. If the preset tuning style is not to your liking, the 3 self-define PEQ (Parametric Equalizer) designs will help to fine adjust to your favorite listening style.
*EQ only works in Bluetooth mode.
Refreshingly modern,
custom stand
The included custom stand not only reduces the amount of space the K9 Pro ESS takes on your desktop, it also allows for more efficient dissipation of heat through convection – making the stand a true example of both form and function.
A true Renaissance man
Connect to home audio setup (desktop USB audio + active speakers)
App-controllable desktop amp Built-in Bluetooth Low Energy (BLE) technology allows you to use the FiiO Control App to control functions like filter selection, channel balance, etc. even when not in Bluetooth mode.
Side-mounted Type-C port for easy connection to mobile device
RCA+XLR balanced line out (for active speakers, monitor speakers, external amplifiers)
Connect to mobile devices (players, computers)
Drive power-hungry headphones (desktop USB audio + Headphones)
Dealers selling FiiO near you
FiiO K9 Pro ESS
FiiO K9 Pro ESS delivers reference-level transparency and surprising bass authority in a compact flagship all‑in‑one. As Sandu Vitalie and Andrew Everard observed, the ESS9038PRO-based DAC paired with THX‑AAA amplification and a linear toroidal supply yields an exceptionally low noise floor and a highly detailed presentation. Bass is strong, tight and textured; midrange stays neutral and honest; treble is open and incisive. Dynamics are explosive and transients quick, while imaging and depth are solid if not hyper‑expansive. Built in CNC‑machined aluminium with balanced 4.4mm/XLR outputs, MQA rendering, LDAC Bluetooth and app control, it’s a complete desktop hub. Ideal for listeners who want a revealing, powerful desktop DAC/amp that outperforms its price — a top pick under $1K.
Pros
- Reference-level clarity with an almost silent noise floor that uncovers fine micro- and macro-detail.
- Powerful, low-distortion THX‑AAA amplification delivering explosive dynamics and fast transient control across a wide range of headphones.
- Premium build and rich feature set — CNC-machined case, ESS DAC with MQA support, LDAC/aptX Bluetooth, balanced outputs and app control for flexible desktop use.
&
Cons
- Soundstage is effective but not as wide or holographic as some pricier Class‑A or tube solutions.
- Very revealing, neutral presentation can be unforgiving with poor masters and may feel bright or fatiguing to some listeners.
Sound Quality
92/100
Dynamics are repeatedly described as effortless and engaging: Sound Advice highlights the amp’s ability to free dynamics from the quietest cymbal taps to full orchestral impact, while Soundnews calls the dynamics “explosive” and says the unit doesn’t run out of breath at high volumes. Reports of strong transient response and no clipping under high drive underpin a top-tier dynamics score.
Noise Floor
95/100
Noise performance is repeatedly lauded: Soundnews explicitly reports “absolute silence in between passages” and an ‘absolute silence’ on the 4.4mm balanced output, while Sound Advice notes careful section separation and shielding to exclude interference. Multiple reviewers’ strong praise for a dead-quiet background supports a reference-level noise-floor score appropriate for sensitive IEMs.
Headphone Compatibility
90/100
The K9 Pro ESS is described as having ‘plenty of power’ (FiiO claim >2W) and is tested with demanding headphones (Audeze LCD-4, Kennerton Rognir, B&W P9 Signature) with no drive issues. Reviews note a fully balanced output (4.4mm) and gain options (reviewer engaged high-gain), so it handles everything from efficient to power-hungry planars well; slight conservatism applied because explicit output-impedance figures (<1Ω) are not cited.
Build Quality
92/100
Both reviews praise robust build: fully CNC-machined aluminium casework, solid mains-powered design and thoughtful internal layout with shielding for analogue/digital separation. Reviewers describe it as premium-feeling and confidently constructed, supporting a high build score.
Features Connectivity
94/100
Starts from a high baseline and adds significant extras: reviewers confirm a high-quality ESS-based DAC, USB input supporting up to 768kHz/32-bit and DSD256, MQA rendering, Bluetooth with LDAC/aptX family support, a 4.4mm balanced headphone output, preamp/line output functionality and app control; the unit also exposes multiple gain settings. That rich feature set places it in the full-featured all-in-one category.
Value for Money
93/100
Reviewers explicitly praise value: Soundnews calls the K9 Pro ESS “dirt cheap” and “probably the best All-In-One combo below $1K,” while Sound Advice calls it a ‘must-listen’ for serious head‑fi. Strong, repeated praise that the unit punches above its price supports an explicit-value score in the high tier.
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