Switching 3 Channel Amps with GCP

[midifail]

Hi there!

I´m using a Mesa Mark V Head here. It has three Channels.
I´d like to control this amp with my trusty GCP and a RJM Mini Amp Gizmo.
The RJM hat a "Group-Function": You can assign the Relais, which control the Channels of the amp, to a Group.
Just one oft the three Relais is then active at a time (CH1 or CH2 or CH3).
This is fine!
But:
How do i use this with my GCP?
If i use three IA-Buttons, i end up having a total random mess of glowing LED for the three switches, which does not correspond to the state of the amp...
Preset Changes do the Job, somehow, but i´d love to be able to switch Channels spontaneously...

Any Ideas, anyone?
Thank you...