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 | Onkyo Muse Y-40 has more power - 75W against 50W into 8 ohms. That is about 1.8dB, which is a small step in loudness but real headroom on peaks. |
| Built-in DAC | A | Onkyo Muse Y-40 has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Streaming | A | Only Onkyo Muse Y-40 has AirPlay 2 and Chromecast. |
| Room to grow | A | Only Onkyo Muse Y-40 offers preamp outputs - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Amplifier class | depends | Onkyo Muse Y-40 is Class D and Rega Brio 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 | Rega Brio takes up about 39% less shelf area (745cm² against 1225cm²). |
| Price | A | Onkyo Muse Y-40 costs less - $1,000 against $1,100 at list. |
| Watts per dollar | A | Onkyo Muse Y-40 is the cheaper watt - about $13 per watt against $22. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Onkyo Muse Y-40 B Rega Brio
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?
Onkyo Muse Y-40 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 already own a DAC or a streamer, the built-in one is money you are paying twice for, and Rega Brio 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.