This works……….need a TRS to Dual TS
SP-H9 – TRS to dual TS cable, connect one end to EXP 1 for expression and the other to EXP 2 for aux switch(4).
In H90 Control, go to Control Assignments > Performance Parameter Mapping, select P switch > Parameter: Act/Byp > Control Source: Aux Switch #4. This will make the switch act/bypass the Program. Make sure you save the Program when you are done.
You can also go to System > External Control and map this globally so the aux switch does act/bypass for every Program.