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 | evenly matched | Effectively the same output - 80W against 72W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Built-in DAC | A | Cambridge CXA81 II has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Streaming | evenly matched | Only Cambridge CXA81 II has Roon. Neither list is longer in a way that matters - check the one service you actually pay for. |
| Analogue inputs | A | Cambridge CXA81 II takes more analogue sources - 5 against 4. |
| Phono stage | depends | Rega Elex-R has a built-in phono stage (MM) and Cambridge CXA81 II does not. Decisive if you own a turntable, completely irrelevant if you do not - and an outboard phono stage is easy to add later either way. |
| Room to grow | evenly matched | The same expansion options on both. |
| Shelf space | depends | Rega Elex-R takes up about 14% less shelf area (1376cm² against 1595cm²), and it is 50mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Cambridge CXA81 II costs less - $1,199 against $1,395 at list. |
| Watts per dollar | A | Cambridge CXA81 II 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 Cambridge CXA81 II B Rega Elex-R
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?
Cambridge CXA81 II is the easier recommendation: it leads on most of the measured areas and costs less. Take Rega Elex-R if one of the "depends" rows above describes your system. If you play records, Rega Elex-R saves you buying a phono stage; if you do not, ignore that row entirely. 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.