The DVD recorders that I've looked at (including my Panasonic DMR-E80) do not support recording Dolby Digital 5.1 - something that I've attributed to Hollywood worrying about piracy more than anything else. You may be able to record Dolby 5.1 with some computer based systems, but I haven't researched it enough to know for sure. There's a pretty significant amount of information available online about HTPC's, which should give some insight on the subject.

I'm a bit surprised that the SA8000HD does not support digital audio output. I know that Scientific Atlanta's digital cable boxes have been a bit behind the curve on supporting digital audio (which is why I've been using Pace boxes for the last few years - Pace's boxes will convert analog audio stations to PCM and pass that to the digital audio output when there isn't a digital audio channel included in the signal). The idea that a high-def cable box doesn't support digital audio output sounds like a misrepresentation to me, or else like a cable provider doing something really stupid.