the only amp head i have Hissues (yeah, hissues!) with, is the JCM 800 model (the Lead 800 in guitarrig), the rest are pretty quiet...
try removing some gain from the amp you´re experiencing hissing with, and boosting it with the Skreamer distortion in front of the amp instead... works pretty nice with the Gratifier at least, especially if you put it in the Raw mode and use an EQ to boost the mids a little and then put the Skreamer after that
