I have the Big 7 without volume control included - straight DAC. I ran it first into my Tube Research Labs Dude preamp (6sn7 tubes with massive tube rectified power supply), but I don't think it had good synergy. Added distortion in a negative way. Switched over to my Aum acoustics Tortuga-based passive pre, and the negative distortion is gone, and transparency is significantly increased. But I do miss a little bit of the weight the Dude added, but that's where signal tube rolling with the Big 7 comes in big time. I'm currently using Gold Lion 300B's which have a much fatter musical presentation than the stock 101D tubes, and totally compensate for the lack of the weight of the Dude. I think that's a HUGE virtue of the Big 7, that it completely transforms its character depending on what tubes you have in there, so you can get the sound you're looking for with even with a passive volume control.