So, I might close this thread early.  I had an enlightening conversation with Arthur tonight regarding tubes.  He has indicated that the 6922 EH tube is the best that he has found for his design in terms of sound quality, reliability, availability and microphony.  Arthur pointed out that even if I was directed towards a 'better' 6922 tube chances are that given there are so many 'fakes' out there I can't be guaranteed of ending up with the real deal.