Fair enough. My system sounds different to me depending on the mood I'm in or how tired I am. The important thing is not the difference in perception but the reason for this difference. Some will claim that solid state equipment goes through enough of a physical transformation during normal use that it actually produces an audible change (always for the better, stops when it's optimal, never going too far). Others will say that we're simply getting used to a new piece of gear. I guess we each have to decide for ourselves which of those two scenarios sounds more real-world plausible and which sounds more fantastical.