I am looking at upgrading the stereo in my 560. Currently there looks like only 4 speakers, two in the dash and two in the rear parcel tray. There is a fader in the centre console which still works and of course a head unit. I am looking at replacing the head unit and installing new and more speakers and probably a small sub. What's the best thing to do for speaker wire - is the existing wiring okay? I can't see where extra speakers would be mounted - are there different door panels with speaker holes? I have been told that these cars should have an amplifier - where would this be located?

Sorry for all the questions.