I've experimented using a compressor model in my HD500 in the fx loop of my amp. The idea was to try and balance out the volume differences when using the volume knob of the guitar, as in, 4-5 for cleans through to 7-8 for dirty, 9-10 for extra crunch/sustain for solos. What I found was the volume difference was too great (with my amp) to make it usable on stage, once I added the compressor I found it really difficult to get an even volume across all guitar volumes settings, without affecting the sound too much. I'm not a fan of the squishy sound, and how the compressor takes away from the attack nuances.
I ended up ditching the experiment and going to some clean boost in the loop, boost clean for clean sections, and also use it as a solo boost.
What I'd really like is a transparent compressor which just makes loud sounds slightly quieter and quiet sounds slightly louder. Any suggestions?