Moth3r said:

I think Burtt is referring to the different decisions made when mixing the "stems" together to create the final mix, rather than adding or removing sound effects.

I still believe what I said here, which is that the Dolby Stereo and 70mm 6-track mixes are identical in terms of content, the only difference being how the stems were combined to make the final mix.

Yes, I absolutely agree with you, maybe wrong of me to call them "additons" when those differences were actually more a case of a different decision in terms of how loud they mixed those effects, the most obvious must be the explosion of the TIE that Han takes out in the trench run, which is almost inaudible in the 35mm mix.