Neo-classical experimental? Soundmass?
Is that a euphemism for when the entire orchestra goes "bleep-bloop-bleep?"
Look for orchestral works by:
Edgar Varese...first and foremost
Ligeti (Check out the orchestral stuff, then go out and get "Mechanical Music" on Sony. So damn awesome)
Xenakis
Earle Brown
George Perle
John Cage
Stockhausen
"The Iron Foundry" by
Mosolov
http://members.lycos.nl/cvdv/Ironfoundrymosolov.html
Hans Werner Henze's symphonies often have "Soundmass" qualities.
Mahler's Sixth Symphony (this has nothing to do with this thread, but if you don't have it already you'd better run out and get Georg Szell's version on Sony...it's, like, seven bucks or something). There's Beethoven's sixth, then there's Mahler's sixth (Webern).