sometimes it's frustrating when this stuff happens. It sounds like your settings are correct. S/PDIF in on the soundcard, also make sure you have "48kHz" (if that's your DAT's rate), highest possible latency, and "independent" checked off.
Have you tried another program to record that may use less resources? I use Wavelab but I'm not sure how it compares to Audition in that respect. You may have to just go part by part through your chain, maybe it's a bad cable or something. You might also find someone to help you, I transfer a lot of DATs to PC via coax.