DHole, your message has me somewhat confused. What do you mean by only getting "analog" signals on most channels. Do you mean only stereo over TOSlink (which would really be digital, not analog), or is there absolutely no signal at all on TOSlink and you have to get sound from the analog RCA L/R jacks?
If all you get is analog stereo over the RCA jacks and aren't getting the signal over TOSlink, could it be your receiver at fault? I know some receivers you have to manually tell them to use the signal from the TOSlink connection instead of the analog RCA connection. My Sony STR-DA30ES had options for TOSlink only, analog only, or autoselect, and this could be set on a per-input basis. Maybe yours has the same but it's set improperly -- DVD is set to look at coax, but somehow your receiver's been set to only look at the analog RCA inputs for your TV sound?
Otherwise, if you are getting signal over TOSlink but it's only occasional, that sounds more like a problem with the receiver, and I think others here may be able to give better advice there than I.