Different price classes - PS Audio PMG S400 costs roughly 5.7x what PS Audio Stellar M700 does. Expect it to lead on paper; the question is whether you will hear the difference through the speakers you own.
| Area | Better | Why |
|---|
| Power | B | PS Audio Stellar M700 has more power - 350W against 200W into 8 ohms. That is about 2.4dB, so it plays usefully louder before it runs out and has more in hand on peaks. |
| Grip on hard loads | evenly matched | Both behave much the same into 4 ohms - output nearly doubles (400W and 700W). |
| Analogue inputs | evenly matched | The same number of line-level inputs (1). |
| Amplifier class | depends | PS Audio PMG S400 is Class A/AB and PS Audio Stellar M700 is Class D. Class D runs cool and draws almost nothing at idle. Modern examples of both measure well - judge by the rest of the page. |
| Shelf space | depends | PS Audio Stellar M700 takes up about 27% less shelf area (1316cm² against 1806cm²), and it is 102mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | B | PS Audio Stellar M700 costs less - $1,749 against $9,999 at list. |
| Watts per dollar | B | PS Audio Stellar M700 is the cheaper watt - about $5 per watt against $50. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A PS Audio PMG S400 B PS Audio Stellar M700
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?
PS Audio Stellar M700 is the easier recommendation: it leads on most of the measured areas and costs less. Take PS Audio PMG S400 if one of the "depends" rows above describes your system. 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 - PS Audio Stellar M700 has the headroom, and headroom is what stops an amplifier hardening up on peaks. At desk distance or in a small room, 200 watts is already more than most people ever use, and the extra 150 watts would be headroom you pay for and never hear - we rate PS Audio Stellar M700 poorly for near-field use for exactly that reason. Think about the whole system: the roughly $8,250 saved by taking the cheaper one would buy better speakers or a subwoofer, which does more for the sound than the difference between two competent amplifiers.
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.