Q lab, I believe, is fairly common for that type of work. I worked on Tear The Curtain, a live theatre/film/multimedia production last year, which is also now about to tour in Toronto (Oct) and we used q lab for all the triggering of music, SFX, and film clips. This particular project had over 100 x Stereo and 5.1 SFX cues, approximately 40 different film clips, most with 5.1 Mix stems, and 20 or so transitional and score music tracks that played between film sections and/or as underscore to live theatre scenes. Many of the triggered music cues and ambience SFX were also programmed to be loopable in case a particular actors performance changed from night to night. In other words, it was extremely complex technically.....that being said, we had an amazing technical stage director, who called each cue along with lighting, rigging, sets, etc. throughout the performance. Her organization and focus throughout each evening was impressive. I would say, IMHO, that q lab, the program, is certainly up to the task for complicated triggering of any kind of media in a live performance, but the tech team has to be top notch as well to ensure that cues are triggered properly during each performance. It is a live performance after all, so no computer is going to be able to follow the intricacies of the actors performance pacing. Only a person can follow the action on stage and direct accordingly.
But to clarify....I'm not a theater guy....I work in film. My only theatre experience is on this show I worked on and I am not familiar with other programs in that industry, but Tear The Curtain was complicated enough that I, at first, had no idea how we were going to pull it off. Q lab was pretty cool once it was all set up.