I cannot import an AC-3 as a backround audio file if I have other AC-3 files in the initial play portion and in the project. When I do it it steps up the estimated space used on the disc several Gigs, thus making it impossible to burn. The ac-3 is only 2 minutes long so very small. I CAN import it as a wav and let DVDA re-encode it so I can make it work that way but obviously a bug. I have recreated it a few times in new projects to be sure.