This seems a bad match to me. The tube amp you'd need to drive the B&W's is going to have to be an absolute brute. I once heard a C-J CAV-50(50W using EL34) with the N805's. Guess what? The tube amp was woefully inadequate. Couple that with the Spectral preamp, and I think you will be very unhappy. If you do insist on a tube amp, you'll need one of the monsters(VTL, VAC, Manley) with a LOT of tubes(8 or 16 per side). When it's time to retube, the money will be on the order of many new amps. And they are not the best sounding tube amps to many tubeophiles. I use tubes almost exclusively. But if you're married to the combination you have now, I have to recommend solid state(YBA, Jeff Rowland, Classe, or maybe even Mark Levinson). Blasphemy? No, I realize tubes are not for all circumstances and it's better to steer someone in what I feel is the right direction, rather than to create another person who complains about tubes. Gotta have tubes? Trade in the preamp towards an all tube rig. I realize you love the Spectral, but you may want to at least try an audtion.