I am not sure what you mean with “Sub in instruments”, but if you are talking about simply changing one for another, there are a few ways to go about it:
- Control full Chains with an expression pedal: Switch between them using the “Invert” Modulator. Connect you expression pedal (here coming in on CC1) to the first Chain ON/OFF button directly, and also connect your CC1 to the handle (little circle) on the “Invert” MODULATOR envelope. Then connect the output of that modulator to the second Chain ON/OFF button.
- The second strategy is to use the fact that: in MG3 it is just the virtual Instrument that is last in the the Chain that is going to sound at all. So you can put two VSTs after each other on the same Chain and control which one should sound by controlling the ON/OFF state button on the last one.
