Exporting a reference mov with mixed down audio doesn’t erase or destroy your original tracks: it creates a new aiff or wav file of the audio. Once you import the sweetened audio back in, you can simply place it on another set of tracks until you’re satisfied with it. Even if you overwrote your original audio in the sequence, you could still get back to it by matchframing the video clip you’re working with.
If you’re asking for a way to preserve the original mix of audio in layers so that you can sweeten the entire mix in your audio program, you can create an OMF file of your audio track. Upon import, your audio program should separate it into layers with each clip having the same name as in the Avid. Audition 1.5 doesn’t read OMF files, but I think 2.0 does. Recent versions of Cakewalk Sonar (I have 4.0) do read OMF files. I’ve tried this with a short film of mine and it was amazing to see all my VO, music, and SFX audio layers intact 🙂