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 | Onkyo Icon A-50 has more power - 110W against 72W into 8 ohms. That is about 1.8dB, which is a small step in loudness but real headroom on peaks. |
| Built-in DAC | B | Onkyo Icon A-50 has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Streaming | B | Only Onkyo Icon A-50 has AirPlay 2, Chromecast and Roon. |
| Room to grow | evenly matched | The same expansion options on both. |
| Shelf space | depends | Rega Elex-R takes up about 16% less shelf area (1376cm² against 1636cm²), and it is 56mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Rega Elex-R costs less - $1,395 against $1,600 at list. |
| Watts per dollar | B | Onkyo Icon A-50 is the cheaper watt - about $15 per watt against $19. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Rega Elex-R B Onkyo Icon A-50
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 Icon A-50 leads across most of the measured areas for a fairly modest premium, so it is the easier pick if the budget stretches. Rega Elex-R is the one to take if it does not. If you already own a DAC or a streamer, the built-in one is money you are paying twice for, and Rega Elex-R 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.