One is a streaming all-in-one and the other is an amplifier. Judge them on how many boxes you want and what you already own, not on the spec sheet alone.
| Area | Better | Why |
|---|
| Power | A | Yamaha R-N600A has more power - 80W against 50W into 8 ohms. That is about 2dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Built-in DAC | evenly matched | Both have a DAC on board with much the same capability. |
| Streaming | evenly matched | Only Denon PMA-900HNE has HEOS. Neither list is longer in a way that matters - check the one service you actually pay for. |
| Analogue inputs | A | Yamaha R-N600A takes more analogue sources - 4 against 3. |
| Room to grow | B | Only Denon PMA-900HNE offers preamp outputs - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Price | A | Yamaha R-N600A costs less - $800 against $949 at list. |
| Watts per dollar | A | Yamaha R-N600A is the cheaper watt - about $10 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 R-N600A 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?
Yamaha R-N600A is the easier recommendation: it leads on most of the measured areas and costs less. Take Denon PMA-900HNE if one of the "depends" rows above describes your system. 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 R-N600A 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 30 watts would be headroom you pay for and never hear.
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.