Have a look at http://wikiwiki.ws/SynApps/index.php/RNSEInRS4. The Canbus wiring is fairly easy given that the car has a TMC box (part of the "old" Navigation). You'll need a cable set from Kufatec or another source. Pls note that the steering wheel buttons will not work and that the RNS-E will not get the time correctly from the dashboard.
my rs4 has nav originally but the one without the tft display so i didnt have canbus wired or a tmc unit.
i bought an rsn-e adapter from kufatec with cd/phone/bose and it came with trailing wires to run to the back of the dis for the can-bus.
if you have rns-d with tmc tuner then you need to bridge the wires to the tmc - at the tmc tuner you connect together the wires from the rns-d that are labelled as can-bus and connect these to the wires running from the tmc tuner to the dis - then you simply use your kufatec adapter and plug everything in including gps antenna.
you probably dont need to code your dis if you are already set up for navi.
adding the oem bluetooth phone was very easy- i wouldnt buy the kufatec adapter as its too expensive and there are far more parts than you need - i would recommend getting the audi mic as this hides in the centre roof panel where there is already an oblong series of little slots - just pull the light cover off and undo the 2 screws to remove the roof console and run the wire behind the head trim where is meets the screen then down the A pillar - the audi mic is directional towards the driver and completely hides which makes for an excellent factory install.
if you update the rns-e code to 360 then you get the phonebook and call syncing over bluetooth and the dis and display shows who is calling and you can dial from the rns-e... all features which make the oem bluetooth install worth having.