IK Multimedia AXE I/O vs Zoom UAC-232

Short answer

More power: the Zoom UAC-232, with 148 mW into 32 Ω; the IK Multimedia AXE I/O has 115 mW. The Zoom UAC-232 drives 2 headphones to 100 dB that the IK Multimedia AXE I/O cannot (Moondrop COSMO, Symphonium Zenith).
Hiss with sensitive IEMs: cannot be compared — neither maker publishes a noise figure.
Output impedance: 520 headphones are left alone by the IK Multimedia AXE I/O under the one-eighth rule but coloured by the Zoom UAC-232 (64 Audio Aspire 1, 64 Audio Fourte, 64 Audio Nio, 517 more).
Price: the IK Multimedia AXE I/O costs $1 more; what that buys on these numbers is set out further down, under What the price difference buys.

Both are audio interfaces, $400 against $399.

The Zoom UAC-232 reaches 100 dB on 563 of the 567 models here, the IK Multimedia AXE I/O on 561.

Every published figure, next to each other

Specification	IK Multimedia AXE I/O	Zoom UAC-232
Power into 32Ω	115 mW	148 mW
Power into 150Ω	60 mW	51 mW
Power into 300Ω	30 mW	28 mW
Power into 600Ω	15 mW	14 mW
Output impedance	<0.1 Ω	12 Ω
Output noise	not published	not published
Price	$400	$399
Headphones it reaches 100 dB on out of 567	561	563

Not published means the maker leaves it out, so that axis cannot be compared.

Where each power figure comes from

Load	IK Multimedia AXE I/O	Zoom UAC-232
32 Ω	Derived	Derived
150 Ω	Derived	Derived
300 Ω	Derived	Derived
600 Ω	Derived	Derived

Neither column is a maker’s power rating at these loads. Of the 280 sources here, 209 publish a figure at at least one load; these two do not, so every row above is derived — between or beyond the loads each maker did publish, holding output voltage as the maker’s own figures imply. The method understates rather than flatters, but it is still arithmetic rather than a rating.

What the labels mean.

The headphones that tell them apart

2 headphones reach 100 dB on the Zoom UAC-232 but not on the IK Multimedia AXE I/O — Moondrop COSMO, Symphonium Zenith.

520 headphones are left alone by the IK Multimedia AXE I/O under the one-eighth rule but coloured by the Zoom UAC-232 (64 Audio Aspire 1, 64 Audio Fourte, 64 Audio Nio, 517 more).

561 of the 567 models here reach 100 dB on both.

Headroom and hiss on 8 models, both sources

Headroom is at a 100 dB SPL peak.

The widest gap on the list is the HiFiMAN Susvara: IK Multimedia AXE I/O has +5 dB of headroom there against +3 dB. 2 dB is about 1.5 times the power, which matters for peaks rather than for how loud the music sits.

The hiss columns are empty for IK Multimedia AXE I/O and Zoom UAC-232 because neither maker publishes no output noise figure.

Headphone	Impedance	Needs	IK Multimedia AXE I/O headroom	Zoom UAC-232 headroom	IK Multimedia AXE I/O hiss	Zoom UAC-232 hiss
Shure SE846	9 Ω	0.04 mW	+29 dB	+30 dB damping	not published	not published
Campfire Audio Andromeda 2020	9 Ω	4.0 mW	+9 dB	+10 dB damping	not published	not published
Audeze LCD-2 Classic	70 Ω	0.79 mW	+22 dB	+21 dB damping	not published	not published
Beyerdynamic DT 1990 Pro (250Ω)	250 Ω	0.63 mW	+18 dB	+17 dB	not published	not published
HiFiMAN HE400se	25 Ω	7.9 mW	+11 dB	+12 dB damping	not published	not published
Audio-Technica ATH-R70X	470 Ω	1.6 mW	+11 dB	+11 dB	not published	not published
Sennheiser HD 600	300 Ω	6.6 mW	+7 dB	+6 dB	not published	not published
HiFiMAN Susvara	60 Ω	50 mW	+5 dB	+3 dB damping	not published	not published

The gap in dollars, against the gap in numbers

The IK Multimedia AXE I/O costs $1 more than the Zoom UAC-232. Out of the 567 models here, that difference buys 520 more models left alone under the one-eighth rule.

It does not run one way only: the cheaper Zoom UAC-232 drives 2 models to 100 dB that the IK Multimedia AXE I/O does not, which is the part worth checking against your own headphones before paying the difference.

Only published figures count here; blank axes are counted separately.