I personally enjoy a lot of avant-garde prog metal artists too, especially Toby Driver's stuff. That said, I'd recommend Ligeti's chamber music: the urgency and even the heaviness (if you can see heaviness beyond distortions, drums and growls) are there too. Also, an uneasy, dark feeling permeates those Ligeti's works I referred to, similar to some of Kayo Dot's ambient-oriented sections. But that's just my opinion and perceptions.
On re-visiting this guy, I'm realizing why I used to hate classical: this guy was one of the first composers I recognized. Then again, anything tied to 2001: A Space Odyssey is going to be pretentious, so I shouldn't be surprised.
So good. I just learned that my piano teacher drove him 60 miles to the airport once, assigned to the task just because he speaks Hungarian...apparently Ligeti's crude Hungarian jokes are so funny they can almost make a person drive off the road.
György Ligeti: Complete Chronological Catalogue in one 16-hour Spotify playlist. http://www.spotifyclassical.com/2012/06/gyorgy-ligeti-complete-chronological.html Plus a mix of 18 etudes taken from 18 albums.