No single best amplifier here. What decides it is what you have to drive, what you need to plug in, and how much of the system you want in one box.
| Area | Better | Why |
|---|
| Power | evenly matched | Effectively the same output - 72W against 80W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Built-in DAC | B | Cambridge Audio CXA81 has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Analogue inputs | B | Cambridge Audio CXA81 takes more analogue sources - 5 against 4. |
| Phono stage | depends | Rega Elex-R has a built-in phono stage (MM) and Cambridge Audio CXA81 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 | Rega Elex-R costs less - $1,395 against $1,499 at list. |
A Rega Elex-R B Cambridge Audio CXA81
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?
The usual trade-off: Cambridge Audio CXA81 measures better, Rega Elex-R costs about 7% less. With most speakers in most rooms that gap is smaller in practice than it looks here. 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.