I'd probably play up the similarities it has with A Chorus Line. You could even go so far as to say, "It's A Chorus Line without the music.

I don't think you need to try to explain the true depth of the show - the insights gained by Circle Mirror Transformation characters, or the "therapy" aspect of the acting class. Although it might be interesting to come with some sort of catch phrase about the fine line between "acting" and "actuality". "Truth" and "Pretend" - where does one end and the other begin?

People are always fascinated by "behind the scenes in show business", so I'd sell it from that direction. It should be easy to promote, and the true meat of the show will become manifest as a pleasant surprise.   

Anyway, them's my thoughts...