I've tried a few tube amps on the the Usher CP 6371 speakers- Prima Luna Prologue 1, Antique Sound Labs AQ1001DT, and Granite Audio 861 monoblocks. These are all push-pull and put out 30-40W. The Usher's are excellent speakers and sound pretty good with each of these, but I don't think I am getting the most out of the Usher's with these amps. My less sensitive previous speakers (Harbeth HL5) seemed better controlled by these tube amps. My guess is that it might take a little more tube power to bring out the best in the Usher's. Read somewhere that the CP series were voiced for solid state amps. I've been amazed at the Usher's bass response, image focus, and detail and dynamics at low volume using a cheap solid state integrated (Jungson 88C). It might be worth considering a tube hybid amp (BAT, Pathos, etc).