You'd think the basics would be covered in the help file... ;-)
I'm just starting out with DVDA and have a project with 48kHz PCM audio. I'd like to "optimize" that, ie. recompress to AC-3, but can't find anywhere to set the bitrate.
192kb/s or 224kb/s would be fine, but knowing my luck it'll default to 640kb/s!
Just render your Vegas project's audio to WAV instead of AC3, and set your DVDA project to use PCM Stereo (File -> Properties -> Audio format). Just to be sure, after you add your files to the project, go to File -> Optimize DVD and make sure each of your audio tracks were detected as WAV. If your project is set to PCM Stereo, and the Recompress Setting type (Audio tab) says "From project", you should be okay.