Burning Down

Check out the American composer George Crumb. A lot of his works are in a similar vein, but they offer a completely different listening experience at the same time. If you like Mikrophonie, the first ideal Crumb piece to check out is Microkosmos (I think that's how it's spelled - you'll find it anyways). It's not electronic (unlike many of Stockhausen's works), instead it is for solo piano. There is a video on YouTube of a performance of this piece which might help you understand how all the different sounds are coming from the piano.

You can also pedal back a few years to an earlier decade in the 20th century and check out Arnold Schoenberg - basically regarded as the father of all avant-garde music in the classical genre.

I would also suggest John Cage, but his music is part of a sub genre called "chance music" and I find that it's more for the seasoned listener of avant-garde music. Save his music for last. I feel the same way about Harry Partch too.

When you get comfortable with music from guys like Stockhausen and Crumb, the next logical step is minimalist music. LaMonte Young, Terry Riley, and Henry Cowell should all be checked out at this stage.

Wow I rambled, but I hope that you can follow it and that my initial suggestion of George Crumb is sufficient. Wikipedia is also a great resource as you can easily find the names of all their contemporaries and successors, even ones who are not well known.

EDIT: oops just saw that you listen to some Cage already. So never mind what I said. I do think that all his pieces that feature non-instruments (he was famous for using radio static to create music) should be saved for last, for example the piece called "Water Walk". But that's just my opinion.