DAC Chip: ESS ES9281 PRO (Single) THX AAA-78 Amp
PCM 24bit MQA, THDN: -110dB, Power: 180mWx2, USB Type-C Male, 3.5mm SE (Microphone: Yes), Aluminum Chassis with SPC Cable

Listening Equipment: Etymotic ER4SR, ER2XR, Shure KSE1500, TIN HiFi P1, Monolith M565C & Beyerdynamic DT990

LISTENING EQUIPMENT USED IMPARTED HUGE INFLUENCE TO SOUND IMPRESSIONS & RATING

💚PROS

Uncolored neutral and natural DAC/Amp with coherent timbre
Balanced dynamics with mild airiness, exceptionally smooth
Great Treble textures with fast decays, solid and vivid, great extensions
Fast Mid-Bass response with rich textures and snappy decays
Tightly controlled deep Sub-Bass with moderate seismic sensation
Very natural tone for chimes, bells, taps and percussions, realistic.
Rich Mids with solid body. Male/Female vocals exhibited great textures.
Realistic, vivid guitars, bass guitars, piano & cello tone with solid bite
Reference grade details retrieval, vivid details, Macro and Micro
Stellar speed and transients handling, effortless
Stellar sibilance resistance, very tolerant of Lo-Fi and shouty recordings
The WIDEST Soundstage among them all, great depth, and headroom
Very-very spacious separation with holographic imaging, 3D for sure
Stellar pairing with sparkly Magnetic Planars, Single BA and Electrostatics
Very futuristic build that is compact, lightweight and with RGB indicators
Drives Tin HiFi P1 Magnetic Planar at 55/100 Volume with ease.

💔CONS

Being THX AAA-78, should have been the strongest amp, but it is NOT. Ovidius B1, S9 Pro, and PEE51 a step stronger and with similar fidelity
THX claimed ability to drive up to 1000Ω, what I heard so far does not convince me that’s the case as my testing does not exceed 250Ω and yet it is already at 70-75/100 region.
Not as organic sounding as the other forerunners, but not digital-ish either. It is no more transparent than the rest of top performers. PAW S1, PEE51 and Ovidius B1 easily offer similar level of transparency.
Not as WOW pairing with single DD IEMs despite stellar with Planars, BA and Electrostatics
No mechanical volume adjuster
The longest bodied dongle so far (at least it is thin and lightweight)
No Balanced Output

VERDICT

THX Onyx. The biggest factor to love THX Onyx is the super WIDE soundstage with stellar holographic imaging, akin to binaural experience. While not exactly razor sharp, the separation of layer is precise and with great depth. This is the most spacious presentation I have heard from a dongle so far – it is actually wider sounding than my Cayin N6ii E02 and Topping D10s/A50s (both in balanced mode). It made my Etymotic ER2XR sounded like a full-sized headphone! However, fidelity wise and coherence, THX Onyx is NO superior to the likes of PEE51, Ovidius B1, PAW S1 or even Shanling UA2/S9, but then again perhaps it is because the nature of being neutral is like that – it doesn’t particularly overdo anything in any area. So, for someone to expect THX Onyx to WOW them with jaw dropping dynamics or aggressive vibe, they would be disappointed. This Onyx is faithful at being natural sounding and will appeal to those preferring finesse over aggression (Questyle M12 capable of that aggressive dynamics). Was about to rate it high but the cons as described in Weaknesses are too glaring to ignore.