I've run a single U70 with my HT3s and listened for long periods. At low to moderate levels the sound was sweet and involving. I don't push it. The few times I've turned it up it's clear it doesn't have the dynamics of my AVA 550exr which I usually use. But I love swapping it out from time to time. The sound is enticing.
To reacquaint yuourself with that "tubey" feeling, you might try hooking just the U70 up for a while.
FWIW.
Craig