After much searching on how to repair my two inoperable headrests on my 03 S8 (one in front, one in rear), I found this fix and decided to try it for the driver's seat. It was pretty much a cinch. Took about one hour in my garage. The hardest part is dealing with the tight spaces.
http://www.audipages.com/files/headrest_a8_fix.pdf

For the rear seat, it was even easier. I removed the bottom of the seat via two screws along the front edge of the seat hidden behind some discrete flaps in the carpet. Now I had access to the two screws at the bottom of the seat back. Once these and the two screws behind the center headrest are out, just "pop" the seat straight up and it will lean forward. you now have access to the innards. All that was required to make my headrest work again was to bend the cable while operating the motor. When I had all the slack out of the cable, my headrest worked just fine. So, I zip-tied the cable to the metal rods in the seat making sure the cable was "taught". Then I put the seats back in in the reverse of how I took them out. This took about 40 minutes from start to finish. Alot better than $800 to a dealer.

These fixes assume your motors aren't burned up or the cable broken but from what I've read, that is rarely the case. If you can hear the motor, chances are these fixes will work for you.

 

Would you be so kind as to explain that procedure on the front seat? Have a 99 A8 with the same problem. Thanks

 

Thanks, found your link in original post.

 

AWSOME!!! I'll be using that, too, as soon as I get my babii back from it's TB service & mirror replacement.

 

Here's a video tutorial showing how to fix headrest in Audi A8 D2:

 

Thank you Jack!!! I followed the steps you show in your video and now my Headrest works!!! I did exactly what you did. Getting the rear motor mounting bolt back into place was a bit tricky. Otherwise, it was really easy, since you showed me what to do. Thank you so much.

Now I can raise it to the top where it needs to be for my head (I'm rather tall). Before, it was stuck in the full down position, where it offered me no protection.