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 | NAD C 389 has more power - 130W against 70W into 8 ohms. That is about 2.7dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Room size | depends | We rate NAD C 389 the better fit for a large room and a very large room, and Marantz PM8006 for a small room. Match the amplifier to the room you actually have, not the one you want. |
| Grip on hard loads | B | Marantz PM8006 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 | B | Marantz PM8006 is the quieter design on paper - 106dB against 95dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | A | NAD C 389 has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Analogue inputs | B | Marantz PM8006 takes more analogue sources - 5 against 3. |
| Room to grow | evenly matched | The same expansion options on both. |
| Amplifier class | depends | NAD C 389 is Class D and Marantz PM8006 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. |
| Price | evenly matched | Priced within a few per cent of each other. |
| Watts per dollar | A | NAD C 389 is the cheaper watt - about $12 per watt against $21. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A NAD C 389 B Marantz PM8006
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. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Marantz PM8006 is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. 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 - NAD C 389 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 70 watts is already more than most people ever use, and the extra 60 watts would be headroom you pay for and never hear - we rate NAD C 389 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.