Short answer
Both are audio interfaces, $2199 against $1749.
The RME ADI-2 Pro FS R reaches 100 dB on 567 of the 567 models here, the RME Fireface UCX II on 564.
| Specification | RME ADI-2 Pro FS R | RME Fireface UCX II |
|---|---|---|
| Power into 32Ω | 3.0 W | 210 mW |
| Power into 150Ω | 634 mW | 45 mW |
| Power into 300Ω | 317 mW | 22 mW |
| Power into 600Ω | 158 mW | 11 mW |
| Output impedance | 0.1 Ω | 1 Ω |
| Output noise | 2.18 µV | not published |
| Price | $2199 | $1749 |
| Headphones it reaches 100 dB on out of 567 | 567 | 564 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Balanced | RME ADI-2 Pro FS R | RME Fireface UCX II |
|---|---|---|
| Socket | balanced | no separate rating |
| Power into 32Ω | 11.8 W derived | — |
| Power into 300Ω | 1.3 W derived | — |
| Output impedance | 0.2 Ω | — |
| Output noise | not published | — |
| Headphones it reaches 100 dB on out of 567 | 567 | — |
Only the RME ADI-2 Pro FS R has a separate balanced rating from its maker; through it, it reaches 100 dB on 567 of the 567 models here. The RME Fireface UCX II may still have a balanced socket — its spec sheet simply gives no figure for one, so there is nothing to put beside it. Derived figures are worked out from the loads the maker did publish.
| Load | RME ADI-2 Pro FS R | RME Fireface UCX II |
|---|---|---|
| 32 Ω | Upper bound | Published |
| 150 Ω | Upper bound | Derived |
| 300 Ω | Upper bound | Derived |
| 600 Ω | Upper bound | Derived |
These two columns are not the same kind of number, and that matters more than the gap between them. RME Fireface UCX II publishes a power rating (at 32 Ω); RME ADI-2 Pro FS R publishes no power figure at any load, only a maximum output voltage, so every milliwatt in its column is a ceiling worked out from that voltage.
A ceiling assumes the amplifier holds that voltage into the load, and nothing on RME ADI-2 Pro FS R’s own sheet says it does. It is the most flattering reading available, and it is used here only because the alternative is a blank. Where the RME ADI-2 Pro FS R column looks the stronger of the two, treat the difference as unproven rather than measured. 24 of the 280 sources here are in that position, with no published power rating at any load.
3 headphones reach 100 dB on the RME ADI-2 Pro FS R but not on the RME Fireface UCX II — Moondrop PARA, Symphonium Crimson, Symphonium Titan.
15 headphones are left alone by the RME ADI-2 Pro FS R under the one-eighth rule but coloured by the RME Fireface UCX II (64 Audio Nio, 64 Audio Volur, Campfire Audio Andromeda 2023, 12 more).
564 of the 567 models here reach 100 dB on both.
Headroom is at a 100 dB SPL peak.
The widest gap on the list is the Sennheiser HD 600: RME ADI-2 Pro FS R has +17 dB of headroom there against +5 dB. 12 dB is about 14 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for RME Fireface UCX II because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | RME ADI-2 Pro FS R headroom | RME Fireface UCX II headroom | RME ADI-2 Pro FS R hiss | RME Fireface UCX II hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +43 dB | +32 dB | 21 dB | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +23 dB | +12 dB | 1 dB | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +32 dB | +21 dB | -1 dB | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +28 dB | +16 dB | -5 dB | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +25 dB | +13 dB | -6 dB | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +21 dB | +10 dB | -12 dB | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +17 dB | +5 dB | -16 dB | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +15 dB | +3 dB | -18 dB | not published |
The RME ADI-2 Pro FS R costs $450 more than the RME Fireface UCX II. Out of the 567 models here, that difference buys 3 more models driven to 100 dB and 15 more models left alone under the one-eighth rule.
Nothing runs the other way: there is no axis here on which the cheaper of the two does better.
Only published figures count here; blank axes are counted separately.
Each in full: RME ADI-2 Pro FS R and RME Fireface UCX II.