These are not the same size of amplifier: Musical Fidelity M6si500 has roughly 3.3x the power of Primare I35 Prisma. That is about 5.2dB, so it is a question of room size and how hard your speakers are to drive, not of one being the better amplifier.
| Area | Better | Why |
|---|
| Power | A | Musical Fidelity M6si500 has more power - 500W against 150W into 8 ohms. That is about 5.2dB - a different class of amplifier rather than a bigger version of the same one, and far more than most rooms will ever ask for. |
| Built-in DAC | B | Primare I35 Prisma has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Analogue inputs | B | Primare I35 Prisma takes more analogue sources - 5 against 4. |
| Amplifier class | depends | Musical Fidelity M6si500 is Class A/B and Primare I35 Prisma 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 | Musical Fidelity M6si500 costs less - $5,499 against $5,795 at list. |
| Watts per dollar | A | Musical Fidelity M6si500 is the cheaper watt - about $11 per watt against $39. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Musical Fidelity M6si500 B Primare I35 Prisma
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. Start with the room. In a large or open-plan room, or with speakers that are hard to drive - low sensitivity, or an impedance that dips - Musical Fidelity M6si500 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 150 watts is already more than most people ever use, and the extra 350 watts would be headroom you pay for and never hear - we rate Musical Fidelity M6si500 poorly for near-field use for exactly that reason. If you already own a DAC or a streamer, the built-in one is money you are paying twice for, and Musical Fidelity M6si500 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.