True, I don't think there's anything significant to be gained from using older versions of the Rancor scene. The compositing, the contrast, and the general picture quality of the '04 in this case are all far better, and switching to older shots just isn't worth it. It's still all the original source material, basically just cleaned up; it's not like there was any CGI that needed replacing.
As far as my 5.1 goes, the inclusion of the Obi-wan scene's deleted music does make it an unofficial hybrid mix, and I understand if that is found objectionable; but I will point out that adywan's ESB used the SE mix, which contains several elements unique to that version that were not present in the original release, most notably several music edits, in addition to various sound effects and stereo surround channels. So strictly speaking that isn't quite 'authentic' either, sound-wise, but it has met with well-deserved acclaim. If Harmy likes how my RotJ sounds, I don't see any reason not to use it as long as an official stereo track was also included; but of course that's just my view.