What with the Bluetooth adaptor, MDI adaptor, now the audio bypass adaptor I have three of them stuffed under the dash now. If I'd thought about it I would have modified the MDI one with the bits needed for the audio. As it is it works like this:

car connector - comes in on the left of the RNS510, ran it straight across the back and it ends on the right side.
audio bypass - connects to the above then runs down the right and back across behind the climate knobs.
MDI, then Bluetooth - these two connect in series and flip across behind the climate knobs too, then up the left to the
RNS510.