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 | A | Yamaha A-S301 has more power - 60W against 45W into 8 ohms. That is about 1.2dB, which is a small step in loudness but real headroom on peaks. |
| Noise floor | B | Denon PMA-600NE is the quieter design on paper - 105dB against 99dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | evenly matched | Both have a DAC on board with much the same capability. |
| Analogue inputs | A | Yamaha A-S301 takes more analogue sources - 6 against 4. |
| Room to grow | evenly matched | The same expansion options on both. |
| Shelf space | depends | Denon PMA-600NE takes up about 17% less shelf area (1405cm² against 1701cm²), and it is 68mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Yamaha A-S301 costs less - $350 against $499 at list. |
| Watts per dollar | A | Yamaha A-S301 is the cheaper watt - about $6 per watt against $11. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Yamaha A-S301 B Denon PMA-600NE
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 A-S301 is the easier recommendation: it leads on most of the measured areas and costs less. Take Denon PMA-600NE if one of the "depends" rows above describes your system. Think about the whole system: the roughly $149 saved by taking the cheaper one would buy better speakers or a subwoofer, which does more for the sound than the difference between two competent amplifiers.
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.