Both are audio interfaces, $1749 against $3199. 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?
On raw power they are level: each reaches 100 dB on 564 of the 567 non-electrostatic models here.
| Specification | RME Fireface UCX II | RME Fireface UFX III |
|---|---|---|
| Power into 32Ω | 210 mW | 200 mW |
| Power into 150Ω | 45 mW | 43 mW |
| Power into 300Ω | 22 mW | 21 mW |
| Power into 600Ω | 11 mW | 11 mW |
| Output impedance | 1 Ω | 2 Ω |
| Output noise | not published | not published |
| Price | $1749 | $3199 |
| Headphones it reaches 100 dB on out of 567 | 564 | 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.
| Load | RME Fireface UCX II | RME Fireface UFX III |
|---|---|---|
| 32 Ω | Published | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Derived | Derived |
| 600 Ω | Derived | Derived |
Both makers publish a power rating, which is less common than the table above makes it look: of the 280 sources here, 209 publish a figure at at least one load and only 2 publish one at all four. RME Fireface UCX II publishes at 32 Ω; RME Fireface UFX III at 32 Ω. Every other row is worked out from those — between two published loads, or beyond them holding voltage constant, which understates rather than flatters.
The two publish at the same loads, which is the one case where the rows of this table can be read straight across.
What each of these labels means, and why a derived figure is still worth printing, is set out in how this data was built.
On power they are interchangeable across this whole database: there is no headphone here that one reaches 100 dB on and the other does not.
74 headphones are left alone by the RME Fireface UCX II under the one-eighth rule but coloured by the RME Fireface UFX III (64 Audio Aspire 1, 64 Audio Fourte, 64 Audio Ocean, 71 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.
The counts above say how many models the two treat differently. This says by how much. The same 8 headphones appear on every page of this kind, ordered from the easiest to drive to the hardest, so a row can be read across pages as well as across columns. Headroom is at a 100 dB SPL peak.
Across all eight the two stay within half a decibel of each other, which is a way of saying that on power this pair is one product.
The hiss columns are empty for RME Fireface UCX II and RME Fireface UFX III because neither maker publishes no output noise figure. That is a gap in the specification, not a quiet amplifier, and it is left blank here rather than filled with a plausible number.
| Headphone | Impedance | Needs | RME Fireface UCX II headroom | RME Fireface UFX III headroom | RME Fireface UCX II hiss | RME Fireface UFX III hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +32 dB | +32 dB damping | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +12 dB | +12 dB damping | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +21 dB | +21 dB | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +16 dB | +16 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +13 dB | +13 dB | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +10 dB | +9 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +5 dB | +5 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +3 dB | +3 dB | not published | not published |
The RME Fireface UFX III costs $1450 more than the RME Fireface UCX II, and on these three axes the money buys nothing: among the 567 models here there is not one that the RME Fireface UFX III handles and the RME Fireface UCX II does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper RME Fireface UCX II leaves 74 models alone under the one-eighth rule that the RME Fireface UFX III does not.
Everything in this paragraph counts only figures the two makers published. An advantage on an axis one of them leaves blank cannot be counted, and is not counted — how often that happens is its own page.
Each has a page of its own with every power figure traced to what the maker published and a full headphone list: RME Fireface UCX II and RME Fireface UFX III. Or put either against your own headphones in the source comparison tool.