The analog audio more than serves my needs. I thought "digital audio" was supposed to be better. In what terms, I don't know.
Also, Apple seems to be pushing "USB digital audio" over analog, at least in OS X. Analog audio-in is already gone on the newer systems and OS X defaults to USB audio-in. I don't think they will get rid of analog audio-out any time soon, but I'd like to see how USB audio-out fares. Does it suck [CPU cycles] badly, on OS 9, or X?