I think like this.
We have speakers that has efficiency ex 86 db/w/m.
So we will use more or less 1 watt to reach our desired sound pressure in 86db.
Therefore if we use 5w amp OR 500w amplifier we will ALWAYS be using ~1w disregarding what ever of amp you're using.
But I am not saying that a 5w amp is enough that is not my point.
When looking at what Paul M at PS audio is saying.
- A over dimension toroidal then the electric circuit needed. Will give be beneficial for sound quality and they usually use bigger than needed.
Another point is that when we know that 98% of all speakers need only one watt to satisfy us.
Why is that so that most of the times it is the biggest and heaviest and most powerful amp is the one that reviewers tend to think is the best sounding one. Even if smaller models in the same amplifier line and brand.
Then what is the difference of all amplifiers that all of them is enough to drive our speakers.
Despite more complex design with more number of transistors (of the same kind) to give more watt out (that we probably do NOT need and probably the higher parts count will not contribute to better sound quality or reliability.)
But on the other hand what do the bigger amplifier have than the smaller ones don't? Yes when we sit there and listening to our 1w then the bigger amplifier has a bigger toroidal and bigger capacitors.
That is the practical difference and the path to better sound quality as i see it. And my two Satoshi.