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. |
| Analogue inputs | B | Yamaha R-S202 takes more analogue sources - 4 against 1. |
| Room to grow | A | Only Fosi Audio MC351 offers preamp outputs and a subwoofer output - 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 has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. 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.