No single best amplifier here. What decides it is what you have to drive, what you need to plug in, and how much of the system you want in one box.
| Area | Better | Why |
|---|
| Power | B | Sonos Amp has more power - 125W against 100W into 8 ohms. That is about 1dB, which is a small step in loudness but real headroom on peaks. |
| Grip on hard loads | B | Sonos Amp holds up better into a 4-ohm load: its output nearly doubles to 250W, where the other increases modestly. That matters with demanding speakers far more than the 8-ohm figure does. |
| Built-in DAC | evenly matched | Both have a DAC on board with much the same capability. |
| Streaming | B | Only Marantz MODEL M1 has Roon and HEOS; only Sonos Amp has Sonos, Qobuz, Apple Music and YouTube Music. |
| Analogue inputs | A | Marantz MODEL M1 takes more analogue sources - 3 against 1. |
| Room to grow | evenly matched | The same expansion options on both. |
| Price | B | Sonos Amp costs less - $699 against $1,000 at list. |
| Watts per dollar | B | Sonos Amp is the cheaper watt - about $6 per watt against $10. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Marantz MODEL M1 B Sonos Amp
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?
Sonos Amp is the easier recommendation: it leads on most of the measured areas and costs less. Take Marantz MODEL M1 if one of the "depends" rows above describes your system. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Sonos Amp is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. Think about the whole system: the roughly $301 saved by taking the cheaper one would buy better speakers or a subwoofer, which does more for the sound than the difference between two competent amplifiers.
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.