Why should the lower output tranny sound so much worse? Is it of a different lam material? The tranny is surely being hit just as hard, so the core is still reacting the same way to the input. Is it a question of loading perhaps?
Given, the noise increase is unwelcome, I can only add that some of my pre-amps actually sound better at higher gains, such as my various Helios modules. I have some 10 and 20dB pads and a constant impedance attenuator so that I can exploit this. Helioses especially really sing with a pad in, and that cannot be a function of the input transformer, which is still getting the same level. FWIW, In my musical area, noise isn't really a problem!
Kindest regards,
ANdyP