These are not the same size of amplifier: Yamaha A-S801 has roughly 3.3x the power of Onkyo A-9110. That is about 5.2dB, so it is a question of room size and how hard your speakers are to drive, not of one being the better amplifier.
| Area | Better | Why |
|---|
| Power | B | Yamaha A-S801 has more power - 100W against 30W into 8 ohms. That is about 5.2dB - a different class of amplifier rather than a bigger version of the same one, and far more than most rooms will ever ask for. |
| Bass control | B | Yamaha A-S801 has the higher damping factor (240 vs 95), which usually means a tighter grip on a woofer. Above about 100 the returns flatten out, so read this as a tendency rather than a ranking. |
| Noise floor | A | Onkyo A-9110 is the quieter design on paper - 103dB against 99dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | Yamaha A-S801 has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Room to grow | evenly matched | The same expansion options on both. |
| Shelf space | depends | Onkyo A-9110 takes up about 20% less shelf area (1434cm² against 1792cm²), and it is 82mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Onkyo A-9110 costs less - $349 against $900 at list. |
| Watts per dollar | B | Yamaha A-S801 is the cheaper watt - about $9 per watt against $12. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Onkyo A-9110 B Yamaha A-S801
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?
The usual trade-off: Yamaha A-S801 measures better, Onkyo A-9110 costs about 61% less. With most speakers in most rooms that gap is smaller in practice than it looks here. Start with the room. In a large or open-plan room, or with speakers that are hard to drive - low sensitivity, or an impedance that dips - Yamaha A-S801 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 30 watts is already more than most people ever use, and the extra 70 watts would be headroom you pay for and never hear - we rate Yamaha A-S801 poorly for near-field use for exactly that reason. If you already own a DAC or a streamer, the built-in one is money you are paying twice for, and Onkyo A-9110 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.