Bvdiman, sorry for any misunderstanding or if I was not clear, as I don't disagree, but absolutely agree with your comments. In the calculations, I did consider a 3db headroom for the amp, which would be 180w for the P-4200. For a 4db headroom, that would be ~225w, and for 5db headroom, ~280w, so just add 1db or 2db to the numbers cited in my previous post.
Also, I have experience with both Class A and A/B Accuphase and Bryston. Again, I recommend getting the P-4200, as I do agree with Dave_72 that it will smoke the Bryston in overall sound quality.