These are not the same size of amplifier: Michi M8 has roughly 2x the power of Michi S5. That is about 3dB, 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 | B | Michi M8 has more power - 1170W against 580W into 8 ohms. That is about 3dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Grip on hard loads | B | Michi M8 holds up better into a 4-ohm load: its output increases strongly to 1800W, where the other increases modestly. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | evenly matched | Much the same signal-to-noise ratio (120dB vs 120dB). |
| Analogue inputs | evenly matched | The same number of line-level inputs (2). |
| Price | evenly matched | Priced within a few per cent of each other. |
| Watts per dollar | B | Michi M8 is the cheaper watt - about $8 per watt against $16. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Michi S5 B Michi M8
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?
Michi M8 has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Michi M8 is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. 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 - Michi M8 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 580 watts is already more than most people ever use, and the extra 590 watts would be headroom you pay for and never hear - we rate Michi M8 poorly for near-field use for exactly that reason.
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.