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 SA45 has more power - 180W against 100W into 8 ohms. That is about 2.6dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Grip on hard loads | evenly matched | Both behave much the same into 4 ohms - output increases strongly (160W and 300W). |
| Noise floor | evenly matched | Much the same signal-to-noise ratio (110dB vs 110dB). |
| Built-in DAC | A | Both decode on board, but only McIntosh MA5300 handles DSD. |
| Streaming | B | Only Arcam SA45 has AirPlay 2, Chromecast and Roon. |
| Room to grow | A | Only McIntosh MA5300 offers a pre-out/main-in loop - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Headphones | depends | Only McIntosh MA5300 has a headphone output. Worth something if you listen late, nothing if you never do. |
| Amplifier class | depends | McIntosh MA5300 is Class A/B and Arcam SA45 is Class G. Class A/B runs warm and is the long-established mainstream choice; 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. |
| Shelf space | depends | Arcam SA45 takes up about 28% less shelf area (1796cm² against 2488cm²), and it is 145mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | B | Arcam SA45 costs less - $5,500 against $6,000 at list. |
| Watts per dollar | B | Arcam SA45 is the cheaper watt - about $31 per watt against $60. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A McIntosh MA5300 B Arcam SA45
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 SA45 has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. 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 - Arcam SA45 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 100 watts is already more than most people ever use, and the extra 80 watts would be headroom you pay for and never hear.
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.