Was going to say the same thing! I hope you paid $10k for one in this condition.
Good luck, the parts costs and labor time can really add up. Just make sure the work is done right.
Google search will be your friend as the search here isn't so good. Use "site:rs6.com parts to fix my broken rs6", or your search term of choice. Go back then forward in your browser if you run into junk links.
Blauparts, Auto Haus AZ, Genuine Audi, all seem rated well for parts.
The metal coolant pipe to replace the broken plastic one can be found on eBay, James Bufkin.
Zimmerman rotors are basically OEM, not branded, a few hundred less. Rotors are directional per side due to cooling veins. Hawk HPS or EBC Yellow pads.
Editing again, you need this, ross-tech.com
Here's a good list of parts and numbers, http://audirssix.com/index.php/overview/maintenance