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 | evenly matched | Effectively the same output - 60W against 60W into 8 ohms is under 1dB, which is not an audible difference in loudness. |
| Grip on hard loads | evenly matched | Both behave much the same into 4 ohms - output increases strongly (100W and 100W). |
| Noise floor | evenly matched | Much the same signal-to-noise ratio (97dB vs 97dB). |
| Built-in DAC | A | Primare I15 Prisma has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Streaming | A | Only Primare I15 Prisma has AirPlay 2, Chromecast and Roon. |
| Analogue inputs | B | Primare I15 MM takes more analogue sources - 5 against 1. |
| Phono stage | depends | Primare I15 MM has a built-in phono stage (MM,MC) and Primare I15 Prisma does not. Decisive if you own a turntable, completely irrelevant if you do not - and an outboard phono stage is easy to add later either way. |
| Room to grow | evenly matched | The same expansion options on both. |
| Shelf space | depends | Primare I15 MM takes up about 13% less shelf area (1200cm² against 1387cm²), and it is 53mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | B | Primare I15 MM costs less - $1,995 against $2,195 at list. |
A Primare I15 Prisma B Primare I15 MM
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?
The usual trade-off: Primare I15 Prisma measures better, Primare I15 MM costs about 9% less. With most speakers in most rooms that gap is smaller in practice than it looks here. If you play records, Primare I15 MM saves you buying a phono stage; if you do not, ignore that row entirely. 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.