Discussions of feature-length audio screening recordings from the first two films can be found in the following links:
70mm screenings
http://originaltrilogy.com/topic/1977-70mm-soundtrack-recording/id/5690/page/1
http://originaltrilogy.com/topic/1977-70mm-Soundtrack-Recording/id/5685
http://originaltrilogy.com/topic/Question-on-the-1977-70mm-Soundtrack-Recording/id/9781
http://originaltrilogy.com/topic/ESB-70mm-Soundtrack-1980-in-theatre-recording/id/12501/page/1
Discussion of another audio recording of a SW (ANH) screening, called ‘Scofield,’ can be found here:
https://originaltrilogy.com/topic/Scofield-version-SW-theater-recording-1977-Released/id/14077
http://originaltrilogy.com/forum/topic.cfm/Is-this-amateur-audio-recording-of-any-use/topic/14000/