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 | B | NAD M10 V3 has more power - 100W against 70W into 8 ohms. That is about 1.5dB, which is a small step in loudness but real headroom on peaks. |
| Grip on hard loads | A | Marantz Model 40n holds up better into a 4-ohm load: its output increases modestly to 100W, where the other barely increases. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | A | Marantz Model 40n is the quieter design on paper - 106dB against 90dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | Both decode on board, but only NAD M10 V3 handles MQA. |
| Streaming | evenly matched | Only Marantz Model 40n has HEOS; only NAD M10 V3 has BluOS. Neither list is longer in a way that matters - check the one service you actually pay for. |
| Room to grow | evenly matched | The same expansion options on both. |
| Headphones | depends | Only Marantz Model 40n has a headphone output. Worth something if you listen late, nothing if you never do. |
| Amplifier class | depends | Marantz Model 40n is Class A/B and NAD M10 V3 is Class D. Class A/B runs warm and is the long-established mainstream choice; Class D runs cool and draws almost nothing at idle. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | NAD M10 V3 takes up about 71% less shelf area (606cm² against 2126cm²), and it is 203mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | evenly matched | Priced within a few per cent of each other. |
| Watts per dollar | B | NAD M10 V3 is the cheaper watt - about $25 per watt against $36. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Marantz Model 40n B NAD M10 V3
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?
NAD M10 V3 has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Marantz Model 40n 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 interface feels 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.