Different price classes - Arcam A5+ costs roughly 2x what Rotel A10 MKII does. Expect it to lead on paper; the question is whether you will hear the difference through the speakers you own.
| Area | Better | Why |
|---|
| Power | evenly matched | Effectively the same output - 50W against 50W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Speaker load rating | B | Arcam A5+ is rated down to 4 ohms against 8, so it is the safer partner for a low-impedance speaker. |
| Noise floor | B | Arcam A5+ is the quieter design on paper - 106dB against 90dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | evenly matched | Both have a DAC on board with much the same capability. |
| Analogue inputs | A | Rotel A10 MKII takes more analogue sources - 4 against 3. |
| Room to grow | B | Only Arcam A5+ offers preamp outputs - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Price | A | Rotel A10 MKII costs less - $599 against $1,200 at list. |
| Watts per dollar | A | Rotel A10 MKII is the cheaper watt - about $12 per watt against $24. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Rotel A10 MKII 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?
Arcam A5+ is ahead, but on only 1 of the measured areas, and it costs about 100% more. That is a lot of money for a narrow margin - Rotel A10 MKII is the sensible buy unless a specific feature above decides it for you. Think about the whole system: the roughly $601 saved by taking the cheaper one would buy better speakers or a subwoofer, which does more for the sound than the difference between two competent amplifiers.
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.