These are not the same size of amplifier: NAD C 399 has roughly 2.6x the power of NAD C 359S. That is about 4.1dB, so it is a question of room size and how hard your speakers are to drive, not of one being the better amplifier.
| Area | Better | Why |
|---|
| Power | B | NAD C 399 has more power - 180W against 70W into 8 ohms. That is about 4.1dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Room size | depends | We rate NAD C 359S the better fit for desk or near-field listening, a small room and a mid-size room, and NAD C 399 for a large room and a very large room. Match the amplifier to the room you actually have, not the one you want. |
| Grip on hard loads | A | NAD C 359S 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 | NAD C 399 is the quieter design on paper - 95dB against 90dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | Both decode on board. NAD C 399 goes higher - 384kHz against 192kHz. Very few recordings exist above 192kHz, so treat this as headroom, not as sound quality. |
| Streaming | A | Only NAD C 359S has Roon and BluOS. |
| Analogue inputs | A | NAD C 359S takes more analogue sources - 3 against 2. |
| Room to grow | B | Only NAD C 399 offers preamp outputs - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Amplifier class | depends | NAD C 359S is Class A/B and NAD C 399 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 | NAD C 359S costs less - $1,299 against $2,899 at list. |
A NAD C 359S B NAD C 399
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?
NAD C 399 is ahead, but on only 1 of the measured areas, and it costs about 123% more. That is a lot of money for a narrow margin - NAD C 359S is the sensible buy unless a specific feature above decides it for you. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - NAD C 359S is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. Start with the room. In a large or open-plan room, or with speakers that are hard to drive - low sensitivity, or an impedance that dips - NAD C 399 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 70 watts is already more than most people ever use, and the extra 110 watts would be headroom you pay for and never hear - we rate NAD C 399 poorly for near-field use for exactly that reason.
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.