A 660AV is something of an odd duck and therefore used to be a bad candidate for running non-MacOS operating systems on. First thing that comes to mind is NetBSD, and NetBSD's machine status document:
http://www.macbsd.com/macbsd/macbsd-docs/machine-status/

Says both ethernet and sound are broken on that machine.

Click to expand...

I should really update that. Sound doesn't work on any of the m68k Macs in NetBSD except for little "blips" (for lack of a better word - kind of like a really short beep). Ethernet, on the other hand, has worked for ages.

The Mac Linux page optimistically says the 660AV works:
http://mac.linux-m68k.org/status/MAC_MODEL_C660.php

Click to expand...

Unfortunately, Linux is not an OS (LNOS). Debian, which is an OS, has lost official m68k support, but a few people are still working on it. It's unclear how hard it is to bootstrap an m68k machine. Here's the latest status:

http://wiki.debian.org/M68k/Porting

I've been meaning to try to get the latest Debian on an m68k Mac so I can see how I can help, but the picture is not very clear. If anyone runs GNU/Linux on m68k, please let me know!