I don't quite understand what OSX has to do with HDD capacity. My 8600 runs OS9.1, and I have plenty of storage. A total of nearly 180GB with 3 drives to be exact. Since OSX takes up much more space than 9 if I decided to install Jag on here with
XPostFacto(which I don't plan on with a measley 400MHZ/576MB, and an unsupported video card) I would actually end up with
less free storage for apps/audio files.
ATA host cards/drives are dirt cheap these days, and have better performance than the stock busses on all but the last generations of G4s.
The problem I see with the router scenario is bandwidth. Trying to stream multiple tracks of 16/44.1 audio from a single external drive to two different CPU's via any interface looks like a nightmare if not impossible to me.
Don't throw away those old Macs yet though........