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 | B | Cambridge Audio Evo 75 has more power - 75W against 60W into 8 ohms. That is about 1dB, which is a small step in loudness but real headroom on peaks. |
| Room size | depends | We rate Naim Nait 5si the better fit for desk or near-field listening and a small room, and Cambridge Audio Evo 75 for a mid-size room, a large room and a very large room. Match the amplifier to the room you actually have, not the one you want. |
| Built-in DAC | B | Cambridge Audio Evo 75 has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Analogue inputs | A | Naim Nait 5si takes more analogue sources - 4 against 1. |
| Use with a TV | depends | Only Cambridge Audio Evo 75 has HDMI ARC, so the television can drive it directly and one remote controls the volume. If the system is for music only, this changes nothing. |
| Amplifier class | depends | Naim Nait 5si 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. |
| Price | A | Naim Nait 5si costs less - $2,299 against $2,499 at list. |
A Naim Nait 5si 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?
The usual trade-off: Cambridge Audio Evo 75 measures better, Naim Nait 5si costs about 8% less. With most speakers in most rooms that gap is smaller in practice than it looks here. If this sits under a television, Cambridge Audio Evo 75 is the one to buy - HDMI ARC means the TV remote controls the volume and there is no second box in the way. If you already own a DAC or a streamer, the built-in one is money you are paying twice for, and Naim Nait 5si 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.