well, I don't know if I found this out by accident or what. But if you turn all the EQ knobs to (almost) 0, and the master ones as well, you can get the channel volumes up to 3-5 at bearable volumes, and get the amp to sound like it was meant to sound (channel volumes of 4-6 probably, esp. on the OD channel).
Seems easier than adding something in the loop, though it does effect the tone. Setting the three knobs between say 0 and 2 gives a good amount of attenuation vs having the eq knobs at 6 or 10.
Tonal changes too, but not necessarily a bad thing.
This assumes all complaints over fizz are bright cap related (related to the setting of the channel volume)