I know that a few years ago there was a device called the DatPort that could accept digital audio from a coax output on a DAT player can convert it to the USB format. It was supposed to be Mac-compatible, but I don't think there's been any software support for the device in quite a while.
Does anybody know if there is any reasonably priced exertnal device that can convert between coax/optical and USB/firewire? I know that there are PCI cards (and even a PCMIA card) that can do this, but I was planning on getting one of the new iMacs, so I'm going to need an external device.