As for Kevin's recommendations, with due respect, equipment manufacturers use tubes which represent a reliable supply for them (followed by reasonable cost) but are not always the 'best' tube of that type.
I would tend to agree with this statement as it relates to most manufacturers out there. However, my conversations with Kevin regarding use of output tubes in both the Avatar and Auricle Musicblocs lead me to the conclusion that VAC is the exception. Kevin supplied me with quite a bit of information on tube comparisons of output tubes, all of them leading me to believe the VAC selected and tested were the best all around choice. As for signal tubes Kevin always recommended that I try various NOS tubes on the market.
For those interested in trying the new production Gold Lion KT-88 tubes, Roger Modjeski at RAM has quite a supply. IMO he is one of the best at matching tubes to ensure quiet performance and reliability. He and Andy at Vintage Tube Services are my primary tube suppliers.