Thanks for the radio pulling diagrams. That first wedge thingy has me very worried - what did you use?
As for the audio, I can't promise anything, but the attenuator should work great. You might need two if they are connecting the cell audio to all 4 pairs of audio lines (does you cell audio come out of the front AND rear speakers?). The radio volume knob will not work - you will need to set cell volume with the miniature pots in each attenuator. This would be a very cheap and slick solution and is the one I plan on using.
May I ask one other question - does the mute cable provided by the Parrot have the Nissan plugs on the end, or did you have to splice the wires? If they do make a Nissan Bose compatible cable, can this be purchased separately do you know? Thanks again. Howard