Let's try again. When you say turn a preset on and off, you probably mean to put the unit into bypass or active. Normally you would use a MIDI CC (Continuous Controller) to do this.
But, as far as I know, a GCP does not support CC, but will only send MIDI Program Change. To support this limitation, we have added "Pseudo-programs" BYP, ACT and TOG as MIDI map options. Look in the manual under "[RCV MAP] – Create a MIDI Program Change Receive Map".
If this doesn't do it for you, you really have to talk to Voodoo – our MIDI interface is pretty normal. We have many GCP users, so hopefully some will chime in.