Sounds like a nice set-up.
I have had a stand-alone system installed into my A6, headrest based (replacement headrest, you keep the original ones). This way the wiring is minimised, but you could choose the hardwire it, or leave a small connector to plug into the rear-cigar lighter socket for power, up to you.
The screens are really good (with IR headsets), and I got many positive comments from colleagues (i.e. they do not notice it's not the original headrest). Also the screens 'flip back' when not in use, so it's positive from a security point of view too.
Worth a look (
c-vista ltd In-Car Multimedia Entertainment Systems)