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 |
|---|
| Built-in DAC | A | Fosi Audio MC351 has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Phono stage | depends | Yamaha R-S202 has a built-in phono stage and Fosi Audio MC351 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. |
| Room to grow | A | Only Fosi Audio MC351 offers preamp outputs - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Amplifier class | depends | Fosi Audio MC351 is Class D and Yamaha R-S202 is Class A/B. Class D runs cool and draws almost nothing at idle; Class A/B runs warm and is the long-established mainstream choice. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | Fosi Audio MC351 takes up about 84% less shelf area (235cm² against 1506cm²), and it is 219mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Fosi Audio MC351 costs less - $190 against $250 at list. |
A Fosi Audio MC351 B Yamaha R-S202
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?
Fosi Audio MC351 is the easier recommendation: it leads on most of the measured areas and costs less. Take Yamaha R-S202 if one of the "depends" rows above describes your system. If you play records, Yamaha R-S202 saves you buying a phono stage; if you do not, ignore that row entirely. If you already own a DAC or a streamer, the built-in one is money you are paying twice for, and Yamaha R-S202 becomes the more rational buy.
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.