What gear did you use the Mk1 with before, and did you like it then?
Could it be a mismatch with the Pass?
If you don't like the sound I would just sell it and purchase a tube preamp with considerably more tube rolling options.
Being restricted to 101D's (or 6H30's for the matter) is not a good place to be in, IMO, as one of the great benefits of tube gear is tailoring the sound with different tubes.
Perhaps look into the extremely well reviewed $1300+ (depending on options) Linear Tube Audio MZ2 preamp/amp as you could sell the Mk1 and have enough leftover to cover the repairs on Supratek.
I use inexpensive Bottlehead kit gear with really good old production tubes and get really good sound.
Probably the only person who has run Visseaux (engraved base) 2A3's in a pair of Bottlehead Paramours.
DeKay