Please help - system "brightness" problem

I would say to follow Neil's advice and give your new speakers a couple weeks' worth of regular use (if you haven't already) before starting to worry. Speakers exhibit both electrical and mechanical break-in periods, to my mind. From what I know of most of your pieces besides the integrated amp (with which I am familiar by reputation only, and I can see in your "System" that you have a good PC for it), I don't think the rest of your gear is likely to sound intrinsically bright. So my only other guess would be - if the problem doesn't resolve itself with break-in, and if the new speakers are not supposed to have a bright sound (I've never heard or read about them) - that maybe their dispersion pattern will require something different in the way of positioning or room treatments.