Rather than have DVDA do your encoding to mpeg2, use the DVDA templates in Vegas and render to those so you're bringing in the actual file DVDA will need to work with. The templates in Vegas are optimized for best results however, pending the length of your finished video, you may wish to use a bitrate calculator to get the maximum punch of the encode. It's always been touted as best to render from the timeline as mpeg2 and import into DVDA, rather than bring an .avi or .mov or other file into DVDA and let it encode from there.