with the gt8, you can only use the expression switch, exp. pdl, ctl & 2 sub controls/sub exp....
the ctl is momentary, so if you get an fs-6 you'll have 2 axe fx params being able to be on/off (assuming it's set to latching), far as i know you can't use the exp switch to control the wah on/off, and still be able to use the wah fully as exp pedal ... can't use manual banks up & down for anything