"As some of you know I like tubes and while I have yet to own a tube amp I feel it is just a matter of time."
Ken, as you know most folks say the best combo is tube pre and SS amp. But if you can get the right tube amp with some low end grunt, you got something special. That said, some tubes are simply better with the low end muscle control. The AR 6550 were pretty impressive, in my system. The mids and highs lacking. EL34 great with mids and highs, but not the low end. I finally settled on the KT88 which gives me the best of both worlds.
As far as rolling tubes as tone controls go, I agree with you. I never thought of tubes rolling as tone controls. I could make the same arguments for changing any component in my system or even wires for that matter. I have discovered that everything affects the sound even the mood and attitude.
Henry