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 | B | JBL SA550 C has more power - 90W against 60W 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 Primare I15 MM the better fit for desk or near-field listening and a small room, and JBL SA550 C for a mid-size room, a large room and a very large room. Match the amplifier to the room you actually have, not the one you want. |
| Grip on hard loads | evenly matched | Both behave much the same into 4 ohms - output increases strongly (100W and 150W). |
| Noise floor | B | JBL SA550 C is the quieter design on paper - 106dB against 97dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | B | 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 | A | Primare I15 MM takes more analogue sources - 5 against 3. |
| Room to grow | evenly matched | The same expansion options on both. |
| Headphones | depends | Only JBL SA550 C has a headphone output. Worth something if you listen late, nothing if you never do. |
| Amplifier class | depends | Primare I15 MM is Class D and JBL SA550 C is Class G. Class D runs cool and draws almost nothing at idle; Class G/H switches its supply rails to cut the heat a Class A/B design wastes. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | Primare I15 MM takes up about 23% less shelf area (1200cm² against 1565cm²). |
| Price | evenly matched | Priced within a few per cent of each other. |
| Watts per dollar | B | JBL SA550 C is the cheaper watt - about $22 per watt against $33. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Primare I15 MM B JBL SA550 C
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?
JBL SA550 C 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 Primare I15 MM 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.