OK, I've now got Hairy_Hen's 5.1 purist mix. Do I use TS Muxer to add this ac3 to the DVD, as explained in this link?
http://originaltrilogy.com/forum/topic.cfm/Harmys-STAR-WARS-TRILOGY-Partly-Despecialized-Edition-HD-THE-WHOLE-TRILOGY-NOW-AVAILABLE-JEDI-v12-IS-OUT/post/426401/#TopicPost426401