These are not the same size of amplifier: Rotel A12 has roughly 2x the power of Rega io. That is about 3dB, so it is a question of room size and how hard your speakers are to drive, not of one being the better amplifier.
| Area | Better | Why |
|---|
| Power | B | Rotel A12 has more power - 60W against 30W into 8 ohms. That is about 3dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Room size | depends | We rate Rega io the better fit for desk or near-field listening, and Rotel A12 for a very large room. Match the amplifier to the room you actually have, not the one you want. |
| Built-in DAC | B | Rotel A12 has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Analogue inputs | B | Rotel A12 takes more analogue sources - 4 against 2. |
| Room to grow | B | Only Rotel A12 offers preamp outputs - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Shelf space | depends | Rega io takes up about 68% less shelf area (522cm² against 1633cm²), and it is 88mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Rega io costs less - $725 against $800 at list. |
| Watts per dollar | B | Rotel A12 is the cheaper watt - about $13 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 Rega io B Rotel A12
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?
Rotel A12 leads across most of the measured areas for a fairly modest premium, so it is the easier pick if the budget stretches. Rega io is the one to take if it does not. 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 - Rotel A12 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 30 watts is already more than most people ever use, and the extra 30 watts would be headroom you pay for and never hear. If you already own a DAC or a streamer, the built-in one is money you are paying twice for, and Rega io becomes the more rational buy.
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.