i put the volume pedal in 11 rack at the end of the rig and plug the actual pedal into my GCP. i like it this way because i can lower the volume without changing the tone. sometimes i want the wide open volume on the guitar tone, but not that much volume coming out like during a verse and then kick it up during the chorus/bridge/solo.

it seems to work for me.

one thing to be careful about is that you have to change the volume pedal position if you play with or without an expression pedal.

ie edit/back -> scroll to volume pedal -> sw1 -> position. i have become extremely po'd in a rehearsal with no sound coming out until i figured this out and felt like a dumb a$$ afterwards.