I captured the audio from the LaserDiscs as 16-bit 48kHz PCM which IIRC has a bit-rate of about 1.5mbps, so I guess it would be worth doing it as 384kbps DD then. :)

I did some tests this evening when I got home from work to try and find out if the audio I have captured is stereo or matrix surround. I re-captured a small segment of the ROTJ audio using the "First 2 channels", "Second 2 channels" and "Mix 4 channels" settings in my capture software. I have then compared the waveforms at max zoom and to my eye they look identical. So I am now fairly sure its matrix surround aka Dolby Surround aka Dolby ProLogic. Which leaves me in a bit of a pickle as I don't know how to encode this to DD without it becoming stereo. :(