Ideally, a lossless capture of the Laserdisc audio, but I haven’t been able to get my hands on it. I’m not sure if anyone has done a preservation. The 5.1 AC3 mix on the DVD is fine, and I’d recommend including it as well, but it barely takes advantage of the surround channels anyway.
Me neither it’s very expensive (in the 70 USD-100 range). I have up to 3 different people I could send a LD to for capture (one even having a Domesday setup) so if I ever get the LD release I will transfer it.