DVDit! PE will let you put 5.1 AC3 files in your project also, it just won't transcode them for you or play them back when proofing.
I wouldn't feel comfortable recommending either one of these tools, though. Too unstable and unreliable.
Tyler A. Hawes
Audio Intervisual Design
18 Years Integrating for Film, Television, DVD & Music Production
West Hollywood, CA: (323) 845-1155