I want to support prof's comments about using tube gear with the 3.7s. I've noticed than ronkent hasn't responded to this discussion yet, but I remember that he was very happy with the sound from his 3.7s when they were driven by a PS Audio BHK Preamp and BHK 250 power amp. My recent addition of a BHK Preamp (with tube input stage and MOSFET output stage) to my M700 monoblocks (class D, with power to spare) has opened up the soundstage and naturalness of the music being produced by my Thiel 2.2s. The 2.2 is definitely an easier load than the 3.7, though, so not every tube or tube/hybrid amp is going to be an ideal match for the 3.7.