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 | Bluesound POWERNODE N331 has more power - 100W against 76W into 8 ohms. That is about 1.2dB, which is a small step in loudness but real headroom on peaks. |
| Noise floor | A | Bluesound POWERNODE N331 is the quieter design on paper - 102dB against 96dB. Audible mainly with sensitive speakers in a quiet room. |
| Built-in DAC | A | Bluesound POWERNODE N331 has a DAC on board; the other needs an external one, which is another box, another power lead and another purchase. |
| Analogue inputs | B | Musical Fidelity M2si takes more analogue sources - 5 against 2. |
| Phono stage | depends | Musical Fidelity M2si has a built-in phono stage (MM) and Bluesound POWERNODE N331 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. |
| Use with a TV | depends | Only Bluesound POWERNODE N331 has HDMI eARC, 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 Bluesound POWERNODE N331 has a headphone output. Worth something if you listen late, nothing if you never do. |
| Amplifier class | depends | Bluesound POWERNODE N331 is Class D and Musical Fidelity M2si is Class A/B. Class D runs cool and draws almost nothing at idle; 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 | Bluesound POWERNODE N331 takes up about 76% less shelf area (418cm² against 1760cm²), and it is 210mm 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 | Bluesound POWERNODE N331 is the cheaper watt - about $13 per watt against $17. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A Bluesound POWERNODE N331 B Musical Fidelity M2si
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?
Bluesound POWERNODE N331 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 play records, Musical Fidelity M2si saves you buying a phono stage; if you do not, ignore that row entirely. If this sits under a television, Bluesound POWERNODE N331 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.