I don't think that perceived sound quality of most of these "audiophool" products have actually nothing to do with the signal or power quality by itself. It is purely the feeling you get from the product, it affects hugely on the perceived sound quality, and is integral part of their hobby. Quite similar thing when we here examine a guts of measurement equipment for checking the build quality, for comparison, think about the Gossen-Metrawatt rotary switch feeling/sound
I think many audiophools actually know this but they don't care, as long as it subjectively sounds better. Technically, many of respected audiophool products are quite crap from purely technical viewpoint.
Yes, room-speaker interaction is the most difficult thing to cope with. It has become clear that a speaker with perfect on-axis frequency response can sound horrible in normal room, if the response is not proper in off-axis angles. You could take any crap speaker, measure the on-axis impulse response and then build an inverse correcting FIR to make it flat in both magnitude and phase, and use DSP to perform the calculation in realtime. But this will fail miserably in a normal room, due to very bad off-axis response. In fact, off-axis response will become even worse.
There was an experiment here in Finland in 80's or late 70's, where they put a loudspeaker (with straight on-axis frequency response) in an anechoic chamber and recorded the sound with a microphone. It is unbelievably difficult to say from the resulting recording which one is the original and which one is the reproduction through the loudspeaker and microphone. Thus the importance of decent off-axis response was demonstrated to be one of the most important things in loudspeaker design (not so easy as one might think).
Regards,
Janne