Personally I don't think Pass is a good match to
B&W speakers. The combo always sounds too analytical
to me. DNA-2 will be a much better match. Belles 250A
and Odyssey stratos are all very good selections.
First, with the high-end system you have and money your looking to spend on an amp, I wouldn't make any decision on an amp without auditioning them in your system and home. You're mixing a tube preamp with a SS amp, so (while rare) there are tech. issues that may impact performance and proper matching.
Instead of these huge single amplifiers, you may want to consider biamping with two smaller amps. Bi-amping almost always yields better results.
As for McCormack versus Pass, I think the McCormack offers great value, but, for elite systems, the upgrades are a necessity. The Rev A Gold upgrades put this amp in rarefied air (the Gold upgrades being the key to super elite performance). You can't beat Pass craftsmanship though, so either way I think you will be happy.