Thank you all for your helpful responses. I'll make sure to take another good look at the HD 800 once I get my rig together. I'm planning on auditioning them side-by-side with the T1 and HD 700. I've also added the Ultrasone 8 to my auditioning list; they could be a perfect match for me in that they combine small size and high end sound. The Fostex TH900 and Shure 1840 might also be worth listening to.
I ordered my WA6SE along with the 274B and 6GL7 tube upgrades so that I wouldn't have to worry about tube rolling already on day one. Glad to hear that they make a big difference.
My Naim DAC arrived three days ago, and I couldn't be any happier with it. It really is an awesome piece of high end equip. My WA6SE should arrive on Monday if everything goes to plan. Somehow I'll have to fit in some headphone auditioning time between Christmas and New Year festivities