An Xbee might be overkill for your project. I use them for collecting a lot of information forward/back from devices (robots, etc.).
I think a IR system:
or a stomp switch with however many MCUs you may need. You could have a master control MCU or just somebody operating the $5 remote. Also you could hook up a "noise detector" so that the cubes pulse (just a few hundred milliseconds) to the percussion.
Just a thought.