You cannot route individual tracks into a single Soundstage plugin. You can, however, take a stereo track and split it into left and right tracks, and then place those 'performers' individually. Other performers in the room will produce the same sound, creating a sort of wall of sound, much like multiple performers would in a real room.

If you want to route multiple tracks into the same Soundstage plugin (not having individual control of each performer), you can run it on an Aux bus or on the master section.

If you want to place performers in multiple places, you will need to create multiple instances of Soundstage and place each accordingly. (You can save your preset for the first one, then load it for each additional instance of Soundstage.)