Vintage: for old-style Fd2 mid-heavy tones that cut through the mix.
FM: stands for "flat-mids" offering a more natural sound but enhanced for even more transparency. It sounds great on a strat's Neck Pickup, truly spectacular!
CompCut: removes the bounding from the feedback loop allowing for Monster Clean Boost tones and some rougher OD sounds with the OD and Boost knobs turned up.
Normal Clipping:even more asymmetrical, sweeter, more open, no "blanket" over the sound.