Revtim, she should check in the manual: if an output on a DVD deck is labeled as “co-ax”, it is likelier than not a co-ax digital audio output, rather than the co-ax “RF” output such as that used by cable-TV, antennas, plain-jane TV/VCRs, etc.
The problem, of course, derives from combining a guiding principle of the home-electronics industry with a guiding principle of the recorded-entertainment industry, namely (a) people should upgrade everything in the house if just one new gadget is added, and (b) people are all out to pirate precious copyrighted material.