Found an unfortunate incompatibility that I wanted to post in case it saves anyone a gray hair or three...
Doing a 5.1 proj, switched to the Direct Sound Mapper in audio devices to do a quick sync check - wanted the mixdown to listen with headphones & this did the trick. However, with the latest Audigy 2 drivers at least, if you try to scrub anything video with the audio device set this way, VV4c will crash mercilessly.