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 | Rotel S14 has more power - 80W against 60W into 8 ohms. That is about 1.2dB, 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 Rotel S14 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 | Rotel S14 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. |
| Shelf space | depends | Naim Nait 5si takes up about 20% less shelf area (1300cm² against 1629cm²), and it is 76mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Naim Nait 5si costs less - $2,299 against $2,499 at list. |
A Naim Nait 5si B Rotel S14
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: Rotel S14 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 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.