Yea, there is a lot of stuffy answers there...I have an xtc classic and use the bb preamp on channels 2 and 3. Keep the gain on the pedal off and crank it's volume. I adjust the amps gain to sound like an old cranked Marshall and use the pedal for old school metal, hard rock, screaming solo's. Doing it this way also enables you to use channel three as just a solo volume boost if you need it. The volume pot on the guitar is very effective for getting rid of excessive gain as well. It all depends on what you play and like.
Matt is totally correct. I usually use a rc booster for the red and Tone Freak is coming out with a new pedal that is very aggressive but not over the top that would be the perfect voice for the blue channel