What type of disc is it? SACD, DVD-A? Most SACD discs have both 2 channel stereo and 5.1 mixes (unsupported players will only be able to read the stereo portion), but the 5.1 channel tracks are not AIFFs at all. Maybe your Mac can read the TOC (table of contents) that tells it where the tracks begin, and is incorrectly giving them AIFF icons even though they aren't.