Where should someone start exploring 20th century avant garde composers? Let's assume the person is already into ambient, techno, IDM, radiophonics, and contemporary experimental musics.
So we're not looking for what you think are necessarily the "best" pieces, but rather composers and pieces that are good entry points for the open-minded and curious.
Preferably, recommend specific recordings/performances that are currently available in some form.
I'll start by suggesting John Tilbury's 1975 recoding of John Cage's Sonatas & Interludes.
I think this represents a good, moderate introduction to Cage.
What would you suggest?