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 | A | Onkyo Icon A-50 has more power - 110W against 80W into 8 ohms. That is about 1.4dB, which is a small step in loudness but real headroom on peaks. |
| Grip on hard loads | A | Onkyo Icon A-50 holds up better into a 4-ohm load: its output increases strongly to 180W, where the other barely increases. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | A | Onkyo Icon A-50 is the quieter design on paper - 104dB against 98dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | evenly matched | Both have a DAC on board with much the same capability. |
| Streaming | evenly matched | Only Onkyo Icon A-50 has Chromecast; only NAD C 368 BluOS-2i has BluOS. Neither list is longer in a way that matters - check the one service you actually pay for. |
| Room to grow | evenly matched | The same expansion options on both. |
| Amplifier class | depends | Onkyo Icon A-50 is Class A/B and NAD C 368 BluOS-2i 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 | Onkyo Icon A-50 costs less - $1,600 against $1,749 at list. |
| Watts per dollar | A | Onkyo Icon A-50 is the cheaper watt - about $15 per watt against $22. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Onkyo Icon A-50 B NAD C 368 BluOS-2i
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?
Onkyo Icon A-50 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 - Onkyo Icon A-50 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.