Please change your avatar because that one is obnoxious and provides little incentive to help out. I have a Balancing Act with the AD1 output tubes and it sound fantastic with balanced HD800s. I am pretty sure Craig likes the PX-4 best in the BA, and I know it sounds great from shorter listening opportunities. I haven't changed the 6SN7 since I got it, and I cannot even recall what it is. I don't think it has a big influence on the sound in this amp.