I can import Quartz files into M8 -
I just drag & drop them into the media manager.
After I was not able to import AI and PDF files via the menu,
I realised, that it worked w/ drag & drop.
M8 seems to get all the inputs first (MIDI, audio in),
but it doesn't put the signals through to the loops,
which I think are rendered by the QuickTime engine.
Usually a Quartz composition plays 'til you pull the plug,
but after import M8 limits every comp to 30 seconds.
The only workaround is to export everything into
QuickTime files of a desired length.