A valve amplifier against a solid-state one. They are not really rivals: they differ in character, in what they will drive and in what owning them involves, so start there rather than with the watts.
| Area | Better | Why |
|---|
| Power | evenly matched | Effectively the same output - 350W against 300W 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 nearly doubles (700W and 600W). |
| Noise floor | A | PS Audio Stellar M700 is the quieter design on paper - 105dB against 85dB. Audible mainly with sensitive speakers in a quiet room. |
| Analogue inputs | evenly matched | The same number of line-level inputs (1). |
| Amplifier type | depends | PS Audio Stellar M700 is Solid State and PS Audio BHK Mono 300 is Hybrid. Valve designs are usually warmer and softer at the limits and need their tubes replaced eventually; solid state is the lower-maintenance choice. This is a taste and ownership decision, not a quality one. |
| Shelf space | depends | PS Audio Stellar M700 takes up about 15% less shelf area (1316cm² against 1544cm²), and it is 51mm shallower, which is the measurement that decides whether a rack door shuts. |
| Price | A | PS Audio Stellar M700 costs less - $1,749 against $8,499 at list. |
| Watts per dollar | A | PS Audio Stellar M700 is the cheaper watt - about $5 per watt against $28. A blunt measure, and it says nothing about how either sounds, but it is the honest one for raw output. |
A PS Audio Stellar M700 B PS Audio BHK Mono 300
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 BHK Mono 300 if one of the "depends" rows above describes your system. Think about the whole system: the roughly $6,750 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.