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 | B | Arcam A25 has more power - 100W against 80W into 8 ohms. That is about 1dB, which is a small step in loudness but real headroom on peaks. |
| Grip on hard loads | B | Arcam A25 holds up better into a 4-ohm load: its output increases strongly to 165W, where the other barely increases. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | B | Arcam A25 is the quieter design on paper - 106dB against 95dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | A | Both decode on board, but only NAD C 379 BluOS-D handles MQA. |
| Streaming | A | Only NAD C 379 BluOS-D has AirPlay 2, Roon and BluOS. |
| Use with a TV | depends | Only NAD C 379 BluOS-D has HDMI, so the television can drive it directly and one remote controls the volume. If the system is for music only, this changes nothing. |
| Room to grow | A | Only NAD C 379 BluOS-D offers a subwoofer output - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Amplifier class | depends | NAD C 379 BluOS-D is Class D and Arcam A25 is Class G. Class D runs cool and draws almost nothing at idle; Class G/H switches its supply rails to cut the heat a Class A/B design wastes. 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 | B | Arcam A25 is the cheaper watt - about $15 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 NAD C 379 BluOS-D B Arcam A25
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?
Arcam A25 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 - Arcam A25 is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. If this sits under a television, NAD C 379 BluOS-D is the one to buy - HDMI ARC means the TV remote controls the volume and there is no second box in the way.
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.