While it is possible to reference existing events, it’s not currently possible to add event reference sound modules to a multi sound module. We’ve been meaning to add that feature for a while.
Until we do find time to add that feature, there’s another option. First, create an event sound and give it a single parameter. In the parent event, add a randomization modulator to that parameter, so that whenever the event sound is triggered, its parameter value is randomized. Then, on that parameter, lay out reference modules for the existing events you want to randomize between. (Make sure not to leave gaps or have overlap unless you you have some reason to want that.)
Yeah, that’s what I was thinking. That would allow me to “weight” the events by giving them different widths if I want some events to fire more frequently than others.