These are not the same size of amplifier: Yamaha A-S701 has roughly 2x the power of Denon PMA-900HNE. That is about 3dB, 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 | A | Yamaha A-S701 has more power - 100W against 50W into 8 ohms. That is about 3dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Room size | depends | We rate Yamaha A-S701 the better fit for a mid-size room, a large room and a very large room, and Denon PMA-900HNE for desk or near-field listening and a small room. Match the amplifier to the room you actually have, not the one you want. |
| Noise floor | B | Denon PMA-900HNE is the quieter design on paper - 105dB against 99dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | Both decode on board, but only Denon PMA-900HNE handles DSD. |
| Streaming | B | Only Denon PMA-900HNE has AirPlay 2, Roon and HEOS. |
| Analogue inputs | A | Yamaha A-S701 takes more analogue sources - 6 against 3. |
| Room to grow | evenly matched | The same expansion options on both. |
| Price | A | Yamaha A-S701 costs less - $800 against $949 at list. |
| Watts per dollar | A | Yamaha A-S701 is the cheaper watt - about $8 per watt against $19. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Yamaha A-S701 B Denon PMA-900HNE
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. 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-S701 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 50 watts is already more than most people ever use, and the extra 50 watts would be headroom you pay for and never hear - we rate Yamaha A-S701 poorly for near-field use for exactly that reason.
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.