Sorry. I re read your post. Since you are using a TRS with the RS for the aux switch you need a TS out of your expression pedal. I'm using the out of a EB volume pedal with no problems. If you use a dedicated expression pedal it has to be TS not TRS. I think mission makes a TS model for the line6 pedals . That's the issue though. It took me a minute to realize this .