These are not the same size of amplifier: Musical Fidelity M6si500 has roughly 7.1x the power of Naim Uniti Star. That is about 8.5dB, 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 70W into 8 ohms. That is about 8.5dB - a different class of amplifier rather than a bigger version of the same one, and far more than most rooms will ever ask for. |
| Room size | depends | We rate Musical Fidelity M6si500 the better fit for a large room and a very large room, and Naim Uniti Star for desk or near-field listening, a small room and a mid-size room. Match the amplifier to the room you actually have, not the one you want. |
| Built-in DAC | B | Naim Uniti Star has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Analogue inputs | A | Musical Fidelity M6si500 takes more analogue sources - 4 against 1. |
| Use with a TV | depends | Only Naim Uniti Star 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. |
| Headphones | depends | Only Naim Uniti Star has a headphone output. Worth something if you listen late, nothing if you never do. |
| Built-in sources | depends | Naim Uniti Star has a CD player built in. That is one less box if you still play discs or listen to radio, and dead weight if you do not. |
| Shelf space | depends | Naim Uniti Star takes up about 32% less shelf area (1371cm² against 2024cm²), and it is 144mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | evenly matched | Priced within a few per cent of each other. |
| Watts per dollar | A | Musical Fidelity M6si500 is the cheaper watt - about $11 per watt against $81. 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 Naim Uniti Star
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?
Musical Fidelity M6si500 has the edge on paper, though not by much. The rows marked "depends" are more likely to decide this than the score is. 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, 70 watts is already more than most people ever use, and the extra 430 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 this sits under a television, Naim Uniti Star 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.