Well, the main thing is that the XPA-1 worked for you.
I suppose there are things we just can't explain.
Theoretically, if the amps and speakers have a flat frequency repsonse, the sound should be pretty good.
But I guess we're humans, not robots.
We are subject to a lot of things.
I had a similar reaction with my Acurus preamp (fatigue) vs Denon preamp (no fatigue), even though theoretically I should NOT have heard any differences.
Anyway, I think getting five XPA-1s is an awesome idea!
I was thinking of getting five myself, but that is a lot of space and weight.