Note: Route the remote display wire and the RF modulator wire from the front to the back. If you start in the rear you'll find there is not enough space to get the RF modulator box into the dash (ask me how I know this little tidbit).
Remove the radio. If you choose to disconnect the radio power be sure you have the radio unlock code or you'll have no way to unlock the radio from SAFE mode without a trip to the dealer. The factory harness has plenty of wire so you really don't need to disconnect it.
To remove the radio Audi offers a special tool to unlock the radio. I've found that jigsaw blades (with the teeth filed off) also work. Slide the tools into the slots on the radio face then pull the radio straight out. The slanted edge of the tools must be long side to the outside edge of the radio. The removal tools are available from any Audi dealer parts department for about $8
Put a towel or something over your console and A/C controls to keep the radio from scratching things up.
Remove the kick panel by removing the plug for access to the screw. Also remove the screw near the top of the panel. Then, slide the panel back slightly to release a tab near the door sill joint then lift up and out.
Route the wire for the FM modulator through the radio opening in the dash, under the dash, behind the kick panel then under the door sill panels. Route the wire for the remote display as appropriate for your mounting location. The wires are thin so I didn't bother to remove the sill trim but just tucked them underneath.
Tuck the wiring behind the seat then route to the decoder.
To hook up the RF modulator you'll need special cables to connect to the RF modulator box. Audi uses a small flat connector instead of the standard RCAish-looking type connector. The antenna cable set I got from Mobile One audio was labeled specifically for VW/Audi. You'll note that there are two antenna connectors on the back of the radio. We're only interested in the one near the outside edge of the radio.
The Audi specific cables.
Neatly stuff all the wiring in the dash. I wrapped the modulator box in foam to prevent it from rattling around and making noise. Re-install the radio.
I placed the remote display just under the center vents. Double sided tape holds it in position. My original plan was to put it down in front of the ashtray but it was too hard to read so high up on the dash is it's home for now. I have ideas of how to integrate it better into the dash but that may come later if I have the time.
Overall, a very nice addition. I've heard music I haven't heard in years and I often find myself sitting and listening after arriving at my destination. Highly recommend.