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 | A | Arcam A25 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. |
| Room size | depends | We rate Arcam A25 the better fit for a large room and a very large room, and Marantz Model 40n for a small room. Match the amplifier to the room you actually have, not the one you want. |
| Grip on hard loads | A | Arcam A25 holds up better into a 4-ohm load: its output increases strongly to 165W, where the other increases modestly. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | evenly matched | Much the same signal-to-noise ratio (106dB vs 106dB). |
| Built-in DAC | A | Both decode on board. Arcam A25 goes higher - 384kHz against 192kHz. Very few recordings exist above 192kHz, so treat this as headroom, not as sound quality. |
| Streaming | B | Only Marantz Model 40n has AirPlay 2, Roon and HEOS. |
| Analogue inputs | evenly matched | The same number of line-level inputs (3). |
| Use with a TV | depends | Only Marantz Model 40n has HDMI ARC, 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 | B | Only Marantz Model 40n offers a subwoofer output - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Amplifier class | depends | Arcam A25 is Class G and Marantz Model 40n is Class A/B. Class G/H switches its supply rails to cut the heat a Class A/B design wastes; 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 | Arcam A25 takes up about 26% less shelf area (1580cm² against 2126cm²), and it is 117mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Arcam A25 costs less - $1,499 against $2,499 at list. |
| Watts per dollar | A | Arcam A25 is the cheaper watt - about $15 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 Arcam A25 B Marantz Model 40n
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 is the easier recommendation: it leads on most of the measured areas and costs less. Take Marantz Model 40n if one of the "depends" rows above describes your system. 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, Marantz Model 40n 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.