Short answer
Both are audio interfaces, $1495 against $1749.
The Apogee Symphony Desktop reaches 100 dB on 566 of the 567 models here, the RME Fireface UCX II on 564.
| Specification | Apogee Symphony Desktop | RME Fireface UCX II |
|---|---|---|
| Power into 32Ω | 490 mW | 210 mW |
| Power into 150Ω | 145 mW | 45 mW |
| Power into 300Ω | 103 mW | 22 mW |
| Power into 600Ω | 90 mW | 11 mW |
| Output impedance | not published | 1 Ω |
| Output noise | not published | not published |
| Price | $1495 | $1749 |
| 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.
| Load | Apogee Symphony Desktop | RME Fireface UCX II |
|---|---|---|
| 32 Ω | Derived | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Derived | Derived |
| 600 Ω | Published | Derived |
Both makers publish a power rating. Apogee Symphony Desktop publishes at 600 Ω; RME Fireface UCX 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 Apogee Symphony Desktop figure is the maker’s own and at 32 Ω only the RME Fireface UCX II figure is the maker’s own. On those rows the derived number is the one to doubt first.
2 headphones reach 100 dB on the Apogee Symphony Desktop but not on the RME Fireface UCX II — Moondrop PARA, Symphonium Crimson.
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 Audio-Technica ATH-R70X: Apogee Symphony Desktop has +18 dB of headroom there against +10 dB. 8 dB is about 6.4 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Apogee Symphony Desktop and RME Fireface UCX II because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | Apogee Symphony Desktop headroom | RME Fireface UCX II headroom | Apogee Symphony Desktop hiss | RME Fireface UCX II hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +36 dB | +32 dB | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +16 dB | +12 dB | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +25 dB | +21 dB | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +22 dB | +16 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +17 dB | +13 dB | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +18 dB | +10 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +12 dB | +5 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +8 dB | +3 dB | not published | not published |
The RME Fireface UCX II costs $254 more than the Apogee Symphony Desktop, and on these three axes the money buys nothing: among the 567 models here there is not one that the RME Fireface UCX II handles and the Apogee Symphony Desktop does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper Apogee Symphony Desktop drives 2 models to 100 dB that the RME Fireface UCX II does not.
Only published figures count here; blank axes are counted separately.
Each in full: Apogee Symphony Desktop and RME Fireface UCX II.