Hi MrT

I'm no midi guru but I will try to explain how I have my H9 setup with the GCP to work with my EVH 5150III head. Although it might not answer your question…I have my H9 going through the effects loop on my EVH head. My H9 is on all the time, I programmed it to send cc to certain presets to turn the amp effects loop on & off or bypass the H9.

For example,

GCP Preset 1, Clean (Amp channel 1 change via midi) with chorus from H9 Preset 12 in my case with cc effects loop on

CGP Preset 2, Crunch (Amp channel 2 change via midi) dry, H9 is bypass cc effects loop off

CGP Preset 3, Lead (Amp channel 3 change via midi) with short delay from H9 Preset 5 in my case with cc effects loop on

And so on… I'm not sure if this information help with your setup. But It works perfectly with mine.