I thought you might find the information at this site of interest, furtehr to your question about SVCDs and .AC3 audio. It directly contradicts what I read elsewhere a while ago (This site appears to have more plausible
information:http://lea.hamradio.si/~s51kq/V-SVCD-AU.HTM#step4
information:http://lea.hamradio.si/~s51kq/V-SVCD-AU.HTM#step4