I've heard about 5 VGL shows. The most recent one was at the Nokia Theater in Los Angeles, and it sounded so good that I had to ask Jack how many players were on stage. He said 33, suggesting to me that there had to be music pumped over the PA to provide such a rich sound. There are also elements, though, like percussion and other things that are not performed live, and are obviously being played from a recording. I think the fact that VGL uses a click track to coordinate the lights, video, and music makes it easier and more acceptable to have some of the music being pumped through, but then again, VGL is meant to be an event more than it is a traditional orchestral experience.
Regarding the Seattle performance of PLAY!, I wish I could go. Just be sure to watch the news, as I think there's a good chance something very cool will be announced.