Apogee Duet 3 vs RME Babyface Pro FS

Short answer

More power: the Apogee Duet 3, with 1.18 W into 32 Ω; the RME Babyface Pro FS has 374 mW. The Apogee Duet 3 drives 2 headphones to 100 dB that the RME Babyface Pro FS cannot (Moondrop PARA, Symphonium Titan).
Hiss with sensitive IEMs: cannot be compared — the maker of the Apogee Duet 3 publishes no noise figure.
Output impedance: 509 headphones are left alone by the Apogee Duet 3 under the one-eighth rule but coloured by the RME Babyface Pro FS (64 Audio Aspire 1, 64 Audio Fourte, 64 Audio Nio, 506 more).
Price: the Apogee Duet 3 costs $250 less, and wherever both makers publish a figure the RME Babyface Pro FS shows no advantage for the extra money.

Both are audio interfaces, $649 against $899.

The Apogee Duet 3 reaches 100 dB on 567 of the 567 models here, the RME Babyface Pro FS on 565.

Every published figure, next to each other

Specification	Apogee Duet 3	RME Babyface Pro FS
Power into 32Ω	1.2 W	374 mW
Power into 150Ω	252 mW	80 mW
Power into 300Ω	126 mW	40 mW
Power into 600Ω	63 mW	20 mW
Output impedance	0.5 Ω	10 Ω
Output noise	not published	6.3 µV
Price	$649	$899
Headphones it reaches 100 dB on out of 567	567	565

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

Where each power figure comes from

Load	Apogee Duet 3	RME Babyface Pro FS
32 Ω	Upper bound	Upper bound
150 Ω	Upper bound	Upper bound
300 Ω	Upper bound	Upper bound
600 Ω	Upper bound	Upper bound

Neither maker publishes a power rating at any load. Both columns above are ceilings, worked out from a maximum output voltage on the assumption that the amplifier holds it into the load — the most flattering reading available for either. 24 of the 280 sources here are in that position. Whichever of the two looks the stronger on power, the difference is unproven; the output-impedance and noise rows are the ones to go on.

What the labels mean.

The headphones that tell them apart

2 headphones reach 100 dB on the Apogee Duet 3 but not on the RME Babyface Pro FS — Moondrop PARA, Symphonium Titan.

509 headphones are left alone by the Apogee Duet 3 under the one-eighth rule but coloured by the RME Babyface Pro FS (64 Audio Aspire 1, 64 Audio Fourte, 64 Audio Nio, 506 more).

565 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 Sennheiser HD 600: Apogee Duet 3 has +13 dB of headroom there against +8 dB. 5 dB is about 3.2 times the power, which matters for peaks rather than for how loud the music sits.

The hiss columns are empty for Apogee Duet 3 because that maker publishes no output noise figure.

Headphone	Impedance	Needs	Apogee Duet 3 headroom	RME Babyface Pro FS headroom	Apogee Duet 3 hiss	RME Babyface Pro FS hiss
Shure SE846	9 Ω	0.04 mW	+39 dB	+34 dB damping	not published	30 dB
Campfire Audio Andromeda 2020	9 Ω	4.0 mW	+19 dB	+14 dB damping	not published	10 dB
Audeze LCD-2 Classic	70 Ω	0.79 mW	+28 dB	+23 dB damping	not published	9 dB
Beyerdynamic DT 1990 Pro (250Ω)	250 Ω	0.63 mW	+24 dB	+19 dB	not published	4 dB
HiFiMAN HE400se	25 Ω	7.9 mW	+21 dB	+16 dB damping	not published	3 dB
Audio-Technica ATH-R70X	470 Ω	1.6 mW	+17 dB	+12 dB	not published	-3 dB
Sennheiser HD 600	300 Ω	6.6 mW	+13 dB	+8 dB	not published	-7 dB
HiFiMAN Susvara	60 Ω	50 mW	+11 dB	+6 dB damping	not published	-9 dB

The gap in dollars, against the gap in numbers

The RME Babyface Pro FS costs $250 more than the Apogee Duet 3, and on these three axes the money buys nothing: among the 567 models here there is not one that the RME Babyface Pro FS handles and the Apogee Duet 3 does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper Apogee Duet 3 drives 2 models to 100 dB and leaves 509 alone under the one-eighth rule that the RME Babyface Pro FS does not.

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