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 75W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Grip on hard loads | B | Cambridge Audio Evo 75 holds up better into a 4-ohm load: its output nearly doubles to 150W, where the other increases strongly. That matters with demanding speakers far more than the 8-ohm figure does. |
| Built-in DAC | evenly matched | Both have a DAC on board with much the same capability. |
| Streaming | B | Only Cambridge Audio Evo 75 has AirPlay 2, Chromecast and Roon. |
| Analogue inputs | A | Cambridge Audio CXA81 takes more analogue sources - 5 against 1. |
| Room to grow | evenly matched | The same expansion options on both. |
| Amplifier class | depends | Cambridge Audio CXA81 is Class A/B and Cambridge Audio Evo 75 is Class D. Class A/B runs warm and is the long-established mainstream choice; Class D runs cool and draws almost nothing at idle. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | Cambridge Audio Evo 75 takes up about 25% less shelf area (1190cm² against 1595cm²). |
| Price | A | Cambridge Audio CXA81 costs less - $1,499 against $2,499 at list. |
| Watts per dollar | A | Cambridge Audio CXA81 is the cheaper watt - about $19 per watt against $33. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Cambridge Audio CXA81 B Cambridge Audio Evo 75
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. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Cambridge Audio Evo 75 is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. Think about the whole system: the roughly $1,000 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.