You must have a bit-perfect audio capture card; just enable capture audio,set the right frequency under raw capture format (stereo 16bit, 44100Hz for PCM and DTS, 48000hz for AC3). set the S/PDIF input, and then you could start to capture. Obviously, if you capture DTS, you must decode it with some other software, or use SoundOut plugin for AviSynth.

I strongly suggest to resurrect this thread when you have your laserdisc player back, as it's better to post your requests (and receive answers) "near on demand".