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 | Onkyo Icon A-50 has more power - 110W against 70W into 8 ohms. That is about 2dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Grip on hard loads | B | Onkyo Icon A-50 holds up better into a 4-ohm load: its output increases strongly to 180W, where the other increases modestly. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | A | Marantz Model 50 is the quieter design on paper - 113dB against 104dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | Onkyo Icon A-50 has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Streaming | B | Only Onkyo Icon A-50 has AirPlay 2, Chromecast and Roon. |
| Use with a TV | depends | Only Onkyo Icon A-50 has HDMI ARC, 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 | A | Only Marantz Model 50 offers a subwoofer output - which decides whether you can add a subwoofer or a power amplifier later without replacing the box. |
| Shelf space | depends | Onkyo Icon A-50 takes up about 23% less shelf area (1544cm² against 2002cm²), and it is 98mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | B | Onkyo Icon A-50 costs less - $1,600 against $1,800 at list. |
| Watts per dollar | B | Onkyo Icon A-50 is the cheaper watt - about $15 per watt against $26. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Marantz Model 50 B Onkyo Icon A-50
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 is the easier recommendation: it leads on most of the measured areas and costs less. Take Marantz Model 50 if one of the "depends" rows above describes your system. 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. If this sits under a television, Onkyo Icon A-50 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.