I frequently use Performances that are layered with 2 or 3 voices in a live situation. This allows me to easily change the mix of the voices while performing by using the sliders to control the volume.
Now, I want to add an external software synth to the mix and use a slider to control that volume, too.
I can’t find a way to set up the MO6/8 so it can:

1. Allow separate volume control of multiple voices AND
2. Allow MIDI volume control of an external synth.

Using Master, I can set it up to control a Performance AND the external synth with no problem, BUT that does not allow any way to change the relative volume of the Voices in the Performance. The entire pre-set mix of the parts within the Performance can be changed, but not the voices individually.

Can I use the MO6/8 to (using the sliders) control the individual volume for multiple voices in a Performance while separately controlling the volume of an external MIDI synth?