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 |
|---|
| Built-in DAC | A | Both decode on board, but only Marantz M-CR612 handles DSD. |
| Streaming | A | Only Marantz M-CR612 has AirPlay 2 and HEOS. |
| Phono stage | depends | Arcam A5 has a built-in phono stage (MM) and Marantz M-CR612 does not. Decisive if you own a turntable, completely irrelevant if you do not - and an outboard phono stage is easy to add later either way. |
| Room to grow | A | Only Marantz M-CR612 offers a subwoofer output - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Built-in sources | depends | Marantz M-CR612 has a CD player built in. That is one less box if you still play discs or listen to radio, and dead weight if you do not. |
| Amplifier class | depends | Marantz M-CR612 is Class D and Arcam A5 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 | Marantz M-CR612 takes up about 46% less shelf area (849cm² against 1580cm²), and it is 62mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Marantz M-CR612 costs less - $650 against $699 at list. |
A Marantz M-CR612 B Arcam A5
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?
Marantz M-CR612 has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. If you play records, Arcam A5 saves you buying a phono stage; if you do not, ignore that row entirely.
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.