Why does better power = better sound?

Bryon, when you speak of power quality, I assume you are talking about the quality of the AC line, correct? The age old question about why our systems sound better at night? When there is less stress on the power grids and the electricity is better quality? Or dedicated lines taking things like refrigerators or air compressors off the lines of our audio equipment?

If so, I think the answer is just the equipment is better able to perform to the best of it's ability when it is driven with better, cleaner power. When fed dirty power, any piece of gear can struggle. That is why some manufacturer's believe that a battery supply (DC) is the only way to provide true clean power. I believe the answer to your questions 3,4 and 5 is simply that with cleaner power, the equipment is getting what it needs to reveal it's potential sound quality.

I suppose it is similar to how a car performs using different octane levels of gasoline. Yes, in cars too, some manufacturers believe that a battery is the best source for clean power.

Cheers,
John

All the jumbled up frequency hash in the powerline continues on into the power supply. As the power is changed to use by the electronics, it STILL carries way too much of the garbage into the signal. Remember the signal has to be amplified with that very same power. So the actual grunge comes through as signal.
The power supply power actually becomes the amplified signal. If it is pure and clean then the signal will be that much better.
If it still has all sorts of spurious hash and grung not filtered out, then it will just not be as good.

I use two big conditioners and now would not want to be without them.

It probably has to do with non-optimal power supplies in equipment that cannot fully eliminate harmonic impurities or adequately deal with small scale fluctuations in power line frequency.