i dont know if you are able to replace the fn2r dash unless there is a fascia kit available (which i havent heard of) so pretty much your gonna have the stock head unit, which means you dont have to mess around and get to keep the steering wheel controls etc.

just grab a line out converter which coverts the signal that the head unit sends out the speakers to signals which you can use with rca cables. the unit i have atm is the jl audio cleansweep cl441dsp. theres others from rockford fosgate and alpine but the jl audio one did the job for me.

from there on its just the matter of getting amps, speakers, sub and wiring them all together.

hope that helps