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 399 has more power - 180W against 120W into 8 ohms. That is about 1.8dB, which is a small step in loudness but real headroom on peaks. |
| Room size | depends | We rate Rotel RA-1572 MKII the better fit for desk or near-field listening, a small room and a mid-size room, and NAD C 399 for a very large room. Match the amplifier to the room you actually have, not the one you want. |
| Grip on hard loads | A | Rotel RA-1572 MKII holds up better into a 4-ohm load: its output increases strongly to 200W, where the other barely increases. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | A | Rotel RA-1572 MKII is the quieter design on paper - 100dB against 95dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | A | Both decode on board, but only Rotel RA-1572 MKII handles MQA. |
| Streaming | evenly matched | Only Rotel RA-1572 MKII has Roon. Neither list is longer in a way that matters - check the one service you actually pay for. |
| Analogue inputs | A | Rotel RA-1572 MKII takes more analogue sources - 4 against 2. |
| Room to grow | evenly matched | The same expansion options on both. |
| Amplifier class | depends | Rotel RA-1572 MKII 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 | evenly matched | Priced within a few per cent of each other. |
| Watts per dollar | B | NAD C 399 is the cheaper watt - about $11 per watt against $18. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Rotel RA-1572 MKII 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?
Rotel RA-1572 MKII has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - Rotel RA-1572 MKII is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating.
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.