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 | B | NAD C 359S has more power - 70W against 50W into 8 ohms. That is about 1.5dB, which is a small step in loudness but real headroom on peaks. |
| Room size | depends | We rate Arcam A5+ the better fit for desk or near-field listening and a small room, and NAD C 359S 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. |
| Grip on hard loads | B | NAD C 359S holds up better into a 4-ohm load: its output increases strongly to 120W, where the other increases strongly. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | A | Arcam A5+ is the quieter design on paper - 106dB against 90dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | Both decode on board, but only NAD C 359S handles MQA. |
| Streaming | B | Only NAD C 359S has Roon and BluOS. |
| Analogue inputs | evenly matched | The same number of line-level inputs (3). |
| Use with a TV | depends | Only NAD C 359S has HDMI eARC, so the television can drive it directly and one remote controls the volume. If the system is for music only, this changes nothing. |
| Room to grow | evenly matched | Only Arcam A5+ offers preamp outputs; only NAD C 359S offers a subwoofer output - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Shelf space | depends | Arcam A5+ takes up about 15% less shelf area (1483cm² against 1740cm²), and it is 56mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | Arcam A5+ costs less - $1,200 against $1,299 at list. |
| Watts per dollar | B | NAD C 359S is the cheaper watt - about $19 per watt against $24. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Arcam A5+ B NAD C 359S
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 359S leads across most of the measured areas for a fairly modest premium, so it is the easier pick if the budget stretches. Arcam A5+ is the one to take if it does not. 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. If this sits under a television, NAD C 359S is the one to buy - HDMI ARC means the TV remote controls the volume and there is no second box in the way.
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.