OK, I tried Mixdown on the audio tracks in the sequence, but that didn’t solve the problem. By (a lot of) random experimentation, I did, however, find a fix for this problem. For each clip that was missing sound, I did this:
1) I unselected “Make Stereo Pair” for the clip, creating a two seperate mono tracks– a1 and a2.
2) I deleted a2.
3) With only a1 remaining, I did a mixdown via Render Only>Mixdown
4) I copied track a1 in the clip, and pasted it into a2
5) I selected both a1 and a2, and toggled “Make Stereo Pair”.
For whatever reason, this worked. The audio on these clips can now be heard when I play them on my camcorder via firewire.
Now, I’m not sure what combination of these things actually made the audio on these clips play again via firewire. After step #3, I could hear the audio again via firewire and my camcorder. I _also_ – I don’t know if this mattered – muted track a2 before I deleted it. I’m not sure if the mixdown step did anything at all!
This was a devilish problem to troubleshoot, and I hope this info is useful to others who run into it. Please feel free to follow up here if you have questions.