None of the oot ever had 5.1 audio.
Sure Lucasfilm could have made a 5.1 mix for the bonus dvd and had the originals restored in anamorphic instead they just dumped them to disc and called it a day after reencoding the 2 channel lossless PCM to crappy dolby low bitrate 2.0.
The closest thing ever to a 5.1 was the original magnetic six track mixes on the 70mm presentations of the trilogy. The first 5.1 mix was done for the 1997 theatrical special edition, sure someone could use this as a base and edit it for the oot but who wants to do that?
It was on the special editions laserdisc as an ac3 but you needed to decode the analog channel it was stored on through the ac3 rf out of a compatible player and run it through a compatible receiver or a decoder.
Stored at a much lower bitrate than the 2 channel digital PCM track, depends on what you think sounds better.
Ocp's dvds had a home brew audio for star wars, empire and jedi. Not sure too much what he did on empire and jedi, i know he added stuff from the mono mix to star wars from an unrestored audio source probably the ac3 1 channel from the editdroid prototype disc. I think he used audacity a freeware program for the audio.
The thx demo on the star wars disc is fan made and not official, still pretty cool if low res.
These were made before the gout was released, i think he used moth3r's pal transfers, and the 2004 ntsc boxset of dvd's. Mixing Pal and NTSC sources, not sure if he even properly rencoded the pal to ntsc, as i have heard some complaints from people who have seen this set. The Laserdisc transfers with the 2004 or gout with 2004 are not a good match, the colors are all over the place between the versions as is the stark difference in grain and the generation the source was scanned from.
They have to be color corrected frame by frame something mr gilchrist obviously did not do as it would be even more tedious than his digitally painting out the 1997 or 2004 cgi.