Googling around tonight I realized the only guide for upmixing 2.0 audio I can find is still Doom9's very out of date thread ( http://forum.doom9.org/showthread.php?t=83384 ).

The problem is it uses intervideo's processor fx from WinDVD and an older version of ffdshow (which has improved to the point of being able to handle the job all by itself.)

Womble Mpeg Video Wizard will upmix, but dialog is spread across all speakers. Sometimes that is fine, but I suspect most people here are more intersted in Pro Logic II's Movie Mode where dialog is anchored front and center.

Anyway, the guide would pretty much involve GraphEdit (or GraphStudio), ffdshow... and that's it. Sounds simple but there are plenty of options including bitrates to 640kbps, and channels in any combination up to 7.1.