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 | HiFi Rose RA280 has more power - 250W against 180W into 8 ohms. That is about 1.4dB, which is a small step in loudness but real headroom on peaks. |
| Grip on hard loads | evenly matched | Both behave much the same into 4 ohms - output barely increases (180W and 250W). |
| Noise floor | B | HiFi Rose RA280 is the quieter design on paper - 109dB against 95dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | A | NAD C 399 BluOS-D has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Streaming | A | Only NAD C 399 BluOS-D has AirPlay 2, Roon and BluOS. |
| Room to grow | A | Only NAD C 399 BluOS-D offers preamp outputs - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Headphones | depends | Only NAD C 399 BluOS-D has a headphone output. Worth something if you listen late, nothing if you never do. |
| Amplifier class | depends | NAD C 399 BluOS-D is Class D and HiFi Rose RA280 is Class AD. 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 399 BluOS-D costs less - $2,599 against $3,395 at list. |
A NAD C 399 BluOS-D B HiFi Rose RA280
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 BluOS-D has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. If you already own a DAC or a streamer, the built-in one is money you are paying twice for, and HiFi Rose RA280 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.