These are not the same size of amplifier: Musical Fidelity M6si500 has roughly 6.6x the power of Musical Fidelity M2si. That is about 8.2dB, so it is a question of room size and how hard your speakers are to drive, not of one being the better amplifier.
| Area | Better | Why |
|---|
| Power | A | Musical Fidelity M6si500 has more power - 500W against 76W into 8 ohms. That is about 8.2dB - a different class of amplifier rather than a bigger version of the same one, and far more than most rooms will ever ask for. |
| Room size | depends | We rate Musical Fidelity M6si500 the better fit for a large room and a very large room, and Musical Fidelity M2si for desk or near-field listening, a small room and a mid-size room. Match the amplifier to the room you actually have, not the one you want. |
| Analogue inputs | B | Musical Fidelity M2si takes more analogue sources - 5 against 4. |
| Phono stage | depends | Musical Fidelity M2si has a built-in phono stage (MM) and Musical Fidelity M6si500 does not. Decisive if you own a turntable, completely irrelevant if you do not - and an outboard phono stage is easy to add later either way. |
| Shelf space | depends | Musical Fidelity M2si takes up about 13% less shelf area (1760cm² against 2024cm²), and it is 60mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | B | Musical Fidelity M2si costs less - $1,299 against $5,499 at list. |
| Watts per dollar | A | Musical Fidelity M6si500 is the cheaper watt - about $11 per watt against $17. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Musical Fidelity M6si500 B Musical Fidelity M2si
depends neither is better in the abstract - it turns on your room, your system or how you will use them. Only specs published for both amplifiers are judged; anything missing on either side is left out rather than guessed.
Which should you choose?
Musical Fidelity M6si500 is ahead, but on only 1 of the measured areas, and it costs about 4.2x the price. That is a lot of money for a narrow margin - Musical Fidelity M2si is the sensible buy unless a specific feature above decides it for you. Start with the room. In a large or open-plan room, or with speakers that are hard to drive - low sensitivity, or an impedance that dips - Musical Fidelity M6si500 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 76 watts is already more than most people ever use, and the extra 424 watts would be headroom you pay for and never hear - we rate Musical Fidelity M6si500 poorly for near-field use for exactly that reason. If you play records, Musical Fidelity M2si saves you buying a phono stage; if you do not, ignore that row entirely.
What a spec sheet cannot show: how either sounds with your speakers, how the controls feel day to day, and what the app is like to live with - which is where most all-in-one amplifiers are actually won or lost. Power figures are the manufacturers' own and are not measured to a common standard, so treat small differences as noise. If you can hear both, that will tell you more than any row above.