As far as I can tell, you have to use the “bus as track” option. You can then open that video in quicktime and export out a stereo aif file. Then extract that audio and paste it back in over the video in the quicktime app, or back in Media100. The other way is to master it out to tape, and redigitize the audio. It’s kind of a pain, so I’m definitely open to suggestions.
I like Floh’s suggestion about the hardware channel 1/2, which is what I thought the “stereo mix” option was.
GM