Short answer
Both are audio interfaces, $219 against $200.
The MOTU M2 reaches 100 dB on 565 of the 567 models here, the Zoom AMS-44 on 549.
| Specification | MOTU M2 | Zoom AMS-44 |
|---|---|---|
| Power into 32Ω | 333 mW | 30 mW |
| Power into 150Ω | 71 mW | 9.7 mW |
| Power into 300Ω | 36 mW | 5.2 mW |
| Power into 600Ω | 18 mW | 2.7 mW |
| Output impedance | not published | 10 Ω |
| Output noise | not published | not published |
| Price | $219 | $200 |
| Headphones it reaches 100 dB on out of 567 | 565 | 549 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Load | MOTU M2 | Zoom AMS-44 |
|---|---|---|
| 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. Zoom AMS-44 publishes a power rating (at 32 Ω); MOTU M2 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 MOTU M2’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 MOTU M2 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.
16 headphones reach 100 dB on the MOTU M2 but not on the Zoom AMS-44 — HiFiMAN HE-6se V2, HiFiMAN HE6 Remastered, HiFiMAN Susvara, 13 more.
549 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 +5 dB. 10 dB is about 11 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for MOTU M2 and Zoom AMS-44 because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | MOTU M2 headroom | Zoom AMS-44 headroom | MOTU M2 hiss | Zoom AMS-44 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +34 dB | +23 dB damping | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +14 dB | +3 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 | +10 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +15 dB | +5 dB damping | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +12 dB | +3 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +7 dB | -1 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +5 dB | -4 dB damping | not published | not published |
The MOTU M2 costs $19 more than the Zoom AMS-44. Out of the 567 models here, that difference buys 16 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 Zoom AMS-44.