Umm, I have an AA in sound engineering, but I haven't heard the "low resistance on your AC supply" one before.
You might tell him he's better off with low NOISE on his AC. Smoother harmonics, less voltage fluctuation, etc, can have a bearing, but power supplies and conditioners that are BUILT IN to most quality audio equipment these days are very well built. BTW, that is what you usually are paying for when you buy top-end equipment - cleaner circuitry and a more advanced POWER SUPPLY for filtering and smoothing.
Avoid ballasted lighting like the plague.
Iso Grounds dont hurt on really sensitive equipment, but I have yet to "hear" a difference.
Everybody has a little theory...If he insists, I guess you should give him what he wants.
