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 - 50W against 50W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Grip on hard loads | B | Denon PMA-900HNE holds up better into a 4-ohm load: its output increases strongly to 85W, where the other barely increases. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | B | Denon PMA-900HNE is the quieter design on paper - 105dB against 98dB. 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 NAD C 338 has Chromecast; only Denon PMA-900HNE has AirPlay 2, Roon and HEOS. |
| Analogue inputs | B | Denon PMA-900HNE takes more analogue sources - 3 against 2. |
| Room to grow | evenly matched | The same expansion options on both. |
| Amplifier class | depends | NAD C 338 is Class D and Denon PMA-900HNE is Class A/B. Class D runs cool and draws almost nothing at idle; Class A/B runs warm and is the long-established mainstream choice. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | NAD C 338 takes up about 21% less shelf area (1349cm² against 1710cm²), and it is 83mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | NAD C 338 costs less - $799 against $949 at list. |
A NAD C 338 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?
Denon PMA-900HNE leads across most of the measured areas for a fairly modest premium, so it is the easier pick if the budget stretches. NAD C 338 is the one to take if it does not. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Denon PMA-900HNE is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating.
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.