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 | JBL SA550 C has more power - 90W against 70W into 8 ohms. That is about 1.1dB, which is a small step in loudness but real headroom on peaks. |
| Grip on hard loads | A | JBL SA550 C holds up better into a 4-ohm load: its output increases strongly to 150W, where the other increases modestly. That matters with demanding speakers far more than the 8-ohm figure does. |
| Noise floor | B | Marantz Model 50 is the quieter design on paper - 113dB against 106dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | A | JBL SA550 C has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Analogue inputs | B | Marantz Model 50 takes more analogue sources - 5 against 3. |
| Room to grow | B | 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. |
| Amplifier class | depends | JBL SA550 C is Class G and Marantz Model 50 is Class A/B. Class G/H switches its supply rails to cut the heat a Class A/B design wastes; Class A/B runs warm and is the long-established mainstream choice. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | JBL SA550 C takes up about 22% less shelf area (1565cm² against 2002cm²), and it is 106mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | B | Marantz Model 50 costs less - $1,800 against $1,999 at list. |
A JBL SA550 C B Marantz Model 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?
Neither runs away with it - they trade advantages. Let the "depends" rows and the speakers you already own settle it. If your speakers are a difficult load - 4 ohms nominal, big woofers, or a sensitivity in the low 80s - JBL SA550 C is the safer partner, because how an amplifier behaves when the impedance drops matters more than its 8-ohm rating. If you already own a DAC or a streamer, the built-in one is money you are paying twice for, and Marantz Model 50 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.