hei @dudu-lai , thank you very much for the reply!
to follow up on your answer: 
why won't I be able to use GPS or mic? 
looking at product info on aliexpress, i see that the head unit comes with mic  and gps atenna.
can't i just splice the current mic/gps (installed in the car) connections on those cables?
mic is just 2 wires on a 3.5 jack and gps looks like a SMA connector, also 2 wires. that looks like a 5 minute soldering job.