Hard to put "better" into words, but easy to hear. I guess, I mean less mechanical sounding, more organic, more low level detail, a more natural sound to voice and strings. More coherent and better balanced across the frequency spectrum. More real? And in this context I'm generally concerned with voice and acoustic instruments - the criteria might be different for hard rock where other sonic attibutes might come into play. I guess my premise is that less power requires less processing of the source signal and that more information comes through as a result. The need to produce more power creates more challenges for the designer and more complexity. Of course I understand that impedance and sensitivity of the speakers play an important part in this, but I wonder if we lose something in the process of having to drive speakers that are inefficient, have too many x-overs, and have tough impedance curves challenging amplifiers, especially tube amplifiers. I think that amp designers try to make their high power stuff sound as good as their low powered stuff while providing more drive for difficult loads that some speakers present; I think that is one of their biggest design challenges - some suceed better other I expect, but I suspect (this is what I am asking) that lower power is "purer" and closer to the source.