This may too complicated...or just plain stupid, but i thought i'd suggest it anyway.

I was google-ing for some ideas and stumbled upon this image. I looked at it as if it was a top down view of the room and had an idea.

To keep it short: Each speaker plays a different instrument or group of instruments of a certain song. Standing in the center will allow for the combined sounds from each speaker to recreate the entire song with all it's instruments.

Example: left speaker plays only guitar and piano bit; right speaker plays drums and base, top speaker plays the lyrics. At the center you get the entire song combined.
Don't know how well it would work in a big area like the hall, but i'm sure it would work just fine in a small area.

...and we'd probably need an audio editing expert.