I haven't done this but I believe there would be a fair bit of work involved. The HiFi system has a 10 channel amplifier with DSP and equalisation tuned for the car. If you only wanted to swap the head unit you are going to lose the DSP and vehicle specific equalisation and the power output of that radio is 4 x 14W RMS, so you are likely to lose bass punch as the sub woofers are likely to be low sensitivity and 14W RMS is not a lot to drive low sensitivity speakers. You could add an additional 4 channel amplifier, you could even add external DSP like audison, but the price will start to get very high. I haven't heard it but I understand the 10 speaker HiFfi system is considered to be very good, Personally I would stick with the audio system you have.
I assume its the apple car play that attracts you. If you are not bothered about your sat Nav would it not be an option to fit an apple tablet where the sat nav goes and feed into the standard head unit.
