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 80W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Grip on hard loads | B | Cambridge Audio CXA81 holds up better into a 4-ohm load: its output increases strongly to 120W, where the other barely increases. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | B | Cambridge Audio CXA81 is the quieter design on paper - 105dB against 98dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | Both decode on board, but only Cambridge Audio CXA81 handles DSD. |
| Streaming | A | Only NAD C 368 BluOS-2i has AirPlay 2, Roon and BluOS. |
| Analogue inputs | B | Cambridge Audio CXA81 takes more analogue sources - 5 against 2. |
| Phono stage | depends | NAD C 368 BluOS-2i 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. |
| Amplifier class | depends | NAD C 368 BluOS-2i 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 | Cambridge Audio CXA81 takes up about 13% less shelf area (1595cm² against 1840cm²), and it is 53mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | B | Cambridge Audio CXA81 costs less - $1,499 against $1,749 at list. |
A NAD C 368 BluOS-2i 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?
Cambridge Audio CXA81 is the easier recommendation: it leads on most of the measured areas and costs less. Take NAD C 368 BluOS-2i if one of the "depends" rows above describes your system. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Cambridge Audio CXA81 is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. If you play records, NAD C 368 BluOS-2i saves you buying a phono stage; if you do not, ignore that row entirely.
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.