Short answer
Both are audio interfaces, $219 against $210.
The MOTU M2 reaches 100 dB on 565 of the 567 models here, the Roland Rubix22 on 542.
| Specification | MOTU M2 | Roland Rubix22 |
|---|---|---|
| Power into 32Ω | 333 mW | 19 mW |
| Power into 150Ω | 71 mW | 15 mW |
| Power into 300Ω | 36 mW | 9.4 mW |
| Power into 600Ω | 18 mW | 5.4 mW |
| Output impedance | not published | 47 Ω |
| Output noise | not published | not published |
| Price | $219 | $210 |
| Headphones it reaches 100 dB on out of 567 | 565 | 542 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Load | MOTU M2 | Roland Rubix22 |
|---|---|---|
| 32 Ω | Upper bound | Derived |
| 150 Ω | Upper bound | Derived |
| 300 Ω | Upper bound | Derived |
| 600 Ω | Upper bound | Derived |
Neither column is a power rating, and the two are not even weak in the same way. The MOTU M2 figures are ceilings worked out from a maximum output voltage, on the assumption that the amplifier holds it into the load. The Roland Rubix22 figures are worked out from figures its maker did publish — power at other loads, or the voltage printed beside it. The second method understates; the first flatters. That is the wrong way round for reading the table straight across, so a gap in favour of the MOTU M2 is the one to doubt.
23 headphones reach 100 dB on the MOTU M2 but not on the Roland Rubix22 — Audeze LCD-5, Dan Clark Audio AEON 2 Closed, Dan Clark Audio AEON 2 Noire, 20 more.
542 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 HiFiMAN HE400se: MOTU M2 has +15 dB of headroom there against +3 dB. 12 dB is about 17 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for MOTU M2 and Roland Rubix22 because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | MOTU M2 headroom | Roland Rubix22 headroom | MOTU M2 hiss | Roland Rubix22 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +34 dB | +21 dB damping | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +14 dB | +1 dB damping | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +23 dB | +13 dB damping | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +18 dB | +12 dB damping | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +15 dB | +3 dB damping | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +12 dB | +6 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +7 dB | +2 dB damping | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +5 dB | -4 dB damping | not published | not published |
The MOTU M2 costs $9 more than the Roland Rubix22. Out of the 567 models here, that difference buys 23 more models driven to 100 dB.
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: MOTU M2 and Roland Rubix22.