Man, I've done this once, when I was doing a platform-rpg (like Flashback), but I lost everything
I was using the Timeline object, and using the parameters on each step to determine which character was saying. It was working perfectly!
The timeline object is VERY powerful, but it is a bit stiff right now (you can't add step in the middle of the timeline, and you can't rearrange them...)
I'll try to make a .cap this weekend, when I'm free, to show it.