You are right on about experimenting with different tubes in the AH preamp. I just bought a pair of older(1958) Amperex e88cc I am going to experiment with. I found that so far my preamp sounds best with a pair of early 60's Siemens Cca in locations 1 and 3 with a pair of early 70's Siemens A-frame e88cc in 2 and 4. All Cca seemed to be too smooth, lacking in spatiality and air. The AH preamp also responds to power cords. No matter what power cord I try on the preamp, I can hear the difference, for better or for worse. Also, Victor just informed me in an e-mail that Joseph will be announcing this next year a new tweak for all his preamps. Stay tuned for an announcement soon from one of his Beta-testers. I don't know the details of this new tweak.