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 | evenly matched | Effectively the same output - 250W against 235W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Grip on hard loads | evenly matched | Both behave much the same into 4 ohms - output increases strongly (390W and 350W). |
| Noise floor | A | Michi Prestige S430 is the quieter design on paper - 115dB against 103dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | Rotel Diamond RA-6000 has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Phono stage | depends | Rotel Diamond RA-6000 has a built-in phono stage (MM) and Michi Prestige S430 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. |
| Headphones | depends | Only Rotel Diamond RA-6000 has a headphone output. Worth something if you listen late, nothing if you never do. |
| Price | A | Michi Prestige S430 costs less - $3,999 against $4,499 at list. |
A Michi Prestige S430 B Rotel Diamond RA-6000
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?
Neither runs away with it - they trade advantages. Let the "depends" rows and the speakers you already own settle it. If you play records, Rotel Diamond RA-6000 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 Michi Prestige S430 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.