charles ives was doing things like this in the early 20's. i think it was him that had two or more marching bands playing simultaneously but differently. his piece central park in the dark is great. it is supposed to be a representation of all of the sounds one can hear in central park in the dark.
i love the idea that if a musical idea is strong enough it can coexist with another similarly strong musical idea and really work. interdependent music! anthony braxton does stuff like this too.
http://jazzinamerica.org/l_jazzimage...No=1&PhotoID=3