I have a friend who has tried various methods of making backup copies of his DVD-A discs. Basically, the ones without any form of copy protection will copy and play fine, but these are mostly early releases from, um, less desirable labels.
All big label releases and later small label releases have some form of copy protection (at least of those he has tried). The copy protection only affects the hi-rez data. The lo-rez audio (DTS/DD) and visual elements (menus, videos, etc.) still work from the backup discs.