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 - 90W against 100W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Room size | depends | We rate Yamaha A-S1200 the better fit for a small room, and Audiolab 9000A for a large room and a very large room. Match the amplifier to the room you actually have, not the one you want. |
| Grip on hard loads | evenly matched | Both behave much the same into 4 ohms - output increases strongly (150W and 160W). |
| Noise floor | evenly matched | Much the same signal-to-noise ratio (110dB vs 110dB). |
| Built-in DAC | B | Audiolab 9000A has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Analogue inputs | A | Yamaha A-S1200 takes more analogue sources - 6 against 3. |
| Room to grow | B | Only Audiolab 9000A offers a pre-out/main-in loop - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Shelf space | depends | Audiolab 9000A takes up about 28% less shelf area (1518cm² against 2123cm²), and it is 146mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | evenly matched | Priced within a few per cent of each other. |
A Yamaha A-S1200 B Audiolab 9000A
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?
Audiolab 9000A 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 A-S1200 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.