Dave G,
I have a similar setup: RWA modded SB3, Channel Island VMB-1 monoblocks, and Bob Brines FTA-2000; and have been considering adding a tube buffer/pre-amp as well. (Don't need/want extra complication or gain from a pre-amp.) However the winter heating bills (and the bigger need for room treatments in my new digs) are keeping me from pulling the trigger. Have also been looking into 5687 based stuff as having more speed and detail than the 6SN7/12SN7 tubes and have read that the 5687 works best in a SRPP circuit. But I'm not sure who builds such a little beast.