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 |
|---|
| Built-in DAC | B | Both decode on board, but only Cambridge Audio CXA81 handles DSD. |
| Streaming | A | Only Bose Music Amplifier has AirPlay 2 and Chromecast. |
| Amplifier class | depends | Bose Music Amplifier is Class D and Cambridge Audio CXA81 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 | Bose Music Amplifier takes up about 69% less shelf area (500cm² against 1595cm²), and it is 147mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Bose Music Amplifier costs less - $579 against $1,499 at list. |
A Bose Music Amplifier 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?
Neither runs away with it - they trade advantages. Let the "depends" rows and the speakers you already own settle it. Think about the whole system: the roughly $920 saved by taking the cheaper one would buy better speakers or a subwoofer, which does more for the sound than the difference between two competent amplifiers.
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.