RE: rhythm playing with a MC2300, Bobby was running an Alembic F-2B preamp thru one in 1973 and 1974, before later moving on to an even more ridiculously powerful SS amp: the 1000watt G.A.S. Godzilla.
BABB, is the GT>Mac the only amp you own? IMHO Trey is kinda known for a slightly pushed power tubes sound. My favorite period for him was the early 90's, with his smokin Mesa Mk III rig and also his later Groove Tube rig. The Deluxes he's been using sound a little too pushed for my taste in recent (past 8 years!) stuff I have heard.
"There, in huge black letters, was 'The Grateful Dead'. It just... cancelled my mind out."-Garcia