the thing about whammy effects, is that the normal whammy pedal gets placed before the praemp and multifx "emulations" tend to get placed after (in the fx loop or inbetween the preamp and poweramp). the problem with this is, that if the pitch shifting occurs after the preamp, then the whole sound (harmonics and all) gets shifted up, which can make it sound thin. this doesn't happen when the whammy is in front of the preamp – it's just the source sound (the guitar) that gets shifted – the natural preamp sound and harmonics stay as they are.
