Audient Horizon 8P vs RME Fireface UFX II

Short answer

More power: the Audient Horizon 8P, with 986 mW into 32 Ω; the RME Fireface UFX II has 200 mW. The Audient Horizon 8P drives 2 headphones to 100 dB that the RME Fireface UFX II cannot (Moondrop PARA, Symphonium Crimson).
Hiss with sensitive IEMs: cannot be compared — neither maker publishes a noise figure.
Output impedance: 421 headphones are left alone by the RME Fireface UFX II under the one-eighth rule but coloured by the Audient Horizon 8P (64 Audio Solo, 7Hz Legato, 7Hz Salnotes Zero, 418 more).
Price: the Audient Horizon 8P costs $701 more; what that buys on these numbers is set out further down, under What the price difference buys.

Both are audio interfaces, $3500 against $2799.

The Audient Horizon 8P reaches 100 dB on 566 of the 567 models here, the RME Fireface UFX II on 564.

Every published figure, next to each other

Specification	Audient Horizon 8P	RME Fireface UFX II
Power into 32Ω	986 mW	200 mW
Power into 150Ω	278 mW	43 mW
Power into 300Ω	140 mW	21 mW
Power into 600Ω	71 mW	11 mW
Output impedance	10 Ω	2 Ω
Output noise	not published	not published
Price	$3500	$2799
Headphones it reaches 100 dB on out of 567	566	564

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

Where each power figure comes from

Load	Audient Horizon 8P	RME Fireface UFX II
32 Ω	Derived	Published
150 Ω	Derived	Derived
300 Ω	Derived	Derived
600 Ω	Published	Derived

Both makers publish a power rating. Audient Horizon 8P publishes at 600 Ω; RME Fireface UFX II at 32 Ω. The other rows are worked out from those.

So the two columns are not equally firm row by row: at 600 Ω only the Audient Horizon 8P figure is the maker’s own and at 32 Ω only the RME Fireface UFX II figure is the maker’s own. On those rows the derived number is the one to doubt first.

What the labels mean.

The headphones that tell them apart

2 headphones reach 100 dB on the Audient Horizon 8P but not on the RME Fireface UFX II — Moondrop PARA, Symphonium Crimson.

421 headphones are left alone by the RME Fireface UFX II under the one-eighth rule but coloured by the Audient Horizon 8P (64 Audio Solo, 7Hz Legato, 7Hz Salnotes Zero, 418 more).

564 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 Audio-Technica ATH-R70X: Audient Horizon 8P has +18 dB of headroom there against +9 dB. 8 dB is about 6.6 times the power, which matters for peaks rather than for how loud the music sits.

The hiss columns are empty for Audient Horizon 8P and RME Fireface UFX II because neither maker publishes no output noise figure.

Headphone	Impedance	Needs	Audient Horizon 8P headroom	RME Fireface UFX II headroom	Audient Horizon 8P hiss	RME Fireface UFX II hiss
Shure SE846	9 Ω	0.04 mW	+39 dB damping	+32 dB damping	not published	not published
Campfire Audio Andromeda 2020	9 Ω	4.0 mW	+19 dB damping	+12 dB damping	not published	not published
Audeze LCD-2 Classic	70 Ω	0.79 mW	+29 dB damping	+21 dB	not published	not published
Beyerdynamic DT 1990 Pro (250Ω)	250 Ω	0.63 mW	+24 dB	+16 dB	not published	not published
HiFiMAN HE400se	25 Ω	7.9 mW	+20 dB damping	+13 dB	not published	not published
Audio-Technica ATH-R70X	470 Ω	1.6 mW	+18 dB	+9 dB	not published	not published
Sennheiser HD 600	300 Ω	6.6 mW	+13 dB	+5 dB	not published	not published
HiFiMAN Susvara	60 Ω	50 mW	+11 dB damping	+3 dB	not published	not published

The gap in dollars, against the gap in numbers

The Audient Horizon 8P costs $701 more than the RME Fireface UFX II. Out of the 567 models here, that difference buys 2 more models driven to 100 dB.

It does not run one way only: the cheaper RME Fireface UFX II leaves 421 models alone under the one-eighth rule that the Audient Horizon 8P 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.