You can certainly do asynchronous disk I/O, via SendIO and CheckIO, but you'll
have to go a level below AmigaDOS to the "trackdisk.device", which gives you
direct access to the data-level organization of the disk. That's maybe more
work than you'd like, as you'd have to manage DOS things on your own; it is,
however, a level equivalent to the other things that happen via messages (i.e.
messages talk to devices, not logical units or files).
-Dave Haynie