Given the following: Help Viewer / Control Link /Global and Focus Mapping / Focus Mapping:
"While only one software control can be manipulated at a time by a single hardware control, []"
I conclude it is impossible to link more than 1 parameter of a VST/i to a knob. Experience shows trying to add a parameter to a knob simply replace the previous one.
Feature Request for Studio One 4: Make it possible to link more than 1 parameter to a (physical) knob.