Thanks for clarifying. This can be done with the current software, just not in the way you are attempting to do it.
Program in gain, out gain, and mix can all be assigned to global controllers, but the control source must be a MIDI CC, aux switch, or expression pedal (not a HotKnob).
If you set your expression pedal to control global P input gain, this will accomplish what you are looking for.
https://cdn.eventideaudio.com/manuals/h90/1.5.2/content/appendix/global.html
Let me know if you have any questions.
