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 - 80W against 70W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Grip on hard loads | B | Denon PMA-1700NE holds up better into a 4-ohm load: its output nearly doubles to 140W, where the other increases strongly. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | evenly matched | Much the same signal-to-noise ratio (105dB vs 107dB). |
| Built-in DAC | evenly matched | Both have a DAC on board with much the same capability. |
| Analogue inputs | A | Cambridge Audio CXA81 takes more analogue sources - 5 against 3. |
| Phono stage | depends | Denon PMA-1700NE has a built-in phono stage (MM,MC) 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 | A | Only Cambridge Audio CXA81 offers preamp outputs - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Shelf space | depends | Cambridge Audio CXA81 takes up about 18% less shelf area (1595cm² against 1949cm²), and it is 78mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Cambridge Audio CXA81 costs less - $1,499 against $2,099 at list. |
| Watts per dollar | A | Cambridge Audio CXA81 is the cheaper watt - about $19 per watt against $30. 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 Denon PMA-1700NE
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 Denon PMA-1700NE 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 - Denon PMA-1700NE is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. If you play records, Denon PMA-1700NE 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.