Both are audio interfaces, $899 against $1749. This page puts them side by side on the only three things a maker can be held to — power, output impedance and noise — and then asks the question that actually matters: which headphones do they treat differently?
The RME Babyface Pro FS reaches 100 dB on 565 of the 567 models here, the RME Fireface UCX II on 564.
| Specification | RME Babyface Pro FS | RME Fireface UCX II |
|---|---|---|
| Power into 32Ω | 374 mW | 210 mW |
| Power into 150Ω | 80 mW | 45 mW |
| Power into 300Ω | 40 mW | 22 mW |
| Power into 600Ω | 20 mW | 11 mW |
| Output impedance | 10 Ω | 1 Ω |
| Output noise | 6.3 µV | not published |
| Price | $899 | $1749 |
| Headphones it reaches 100 dB on out of 567 | 565 | 564 |
A figure marked not published is missing from the maker’s own material, which is not the same as being good or bad. Where one of these two publishes a number and the other does not, the comparison on that axis cannot be made at all — and saying so is more useful than guessing.
1 headphone reaches 100 dB on the RME Babyface Pro FS but not on the RME Fireface UCX II — Symphonium Crimson.
495 headphones are left alone by the RME Fireface UCX II under the one-eighth rule but coloured by the RME Babyface Pro FS (64 Audio Aspire 1, 64 Audio Fourte, 64 Audio Ocean, 492 more).
564 of the 567 models here reach 100 dB on both. That is a power count and nothing more; whether either source suits a given headphone also depends on the two lines above.
Each has a page of its own with every power figure traced to what the maker published and a full headphone list: RME Babyface Pro FS and RME Fireface UCX II. Or put either against your own headphones in the source comparison tool.