Upgrading Sophia Electric 91-01 amps

I own a pair of the Sophia 91-01 300B amps and wondered if anyone here has upgraded their Sophias? What aspects of the amps did you focus on and what were the results?
Best way is to either upgrade to Level 05 output transformers

or just buy 91-01 amplifiers if money allows.
You may consider upgrade to level 05 output transformers
or buy high level Sophia Electric 91-03 9105 amplifiers.
Sophia Electric has issued upgrade path for 91-01 owners. Check out at www.sophiaelectric.com