speaking of Varése here are recordings from 57 in ny with Varése conducting a bunch of jazz folks ((Art Farmer (trumpet), Hal McKusik (clarinet, alto sax), Teo Macero (tenor sax), Eddie Bert (trombone), Frank Rehak (trombone), Don Butterfield (tuba), Hall Overton (piano), Charlie Mingus (bass), Ed Shaughnessy (drums), probably John La Porta (alto sax)... We don't know who is on vibes...)) while they freely improvise.
some interesting stuff. this is possibly the beginning of this sort of approach. butch morris being another to do a similar thing but in the 70s and 80s.
http://blog.wfmu.org/freeform/2009/0...zmen-mp3s.html