Right, but the 70mm theatrical track was never in stereo, it was in six-track surround. So the 5.1 upmix more closely approximates the experience of seeing the film in 70mm.

And the earliest non-time-compressed LD releases of Empire and Jedi (both prior to the Japanese Special Collection, where the 1985 mix[es] first appeared if I'm not mistaken) are what Dark_Jedi is using for the theatrical soundtracks.

The theatrical soundtrack for Star Wars was synced by Belbucus a while back, from a similar early non-time-compressed laserdisc.