Mark, you have a pair of big Def Techs, right? That's an aluminum tweeter with a silk surround, a hybrid of sorts. I've heard a whole lot of Def Techs from the tiny to the mammoth. That tweeter, while pretty smooth for aluminum, is a bit bright. It may like your tube amps better, but your midrange drivers, and most of the "music range," may really be benefitting from the speed and damping of the big SS amp. Just a guess. Do you have EQ of any kind in the system? If you do, while you're still using the SS amp, fool around with a slight dip, 3 - 6 db, at around 2k - 5K. You may get ultra sweet, sell your tube amps and take a cruise.
Or not.
Tim
Tim-They are the big Def Techs and I don't find the tweeter to be bright regardless of the amp I'm using. And no, I don't have any equalizers nor do I feel the need for one.