I've the standard head unit with the Harman Kardan speaker syystem. I want to change the head unit but complicated with the amps inside the doors forthe speakers. So does anybody know if there is an interface for a new head unit. It will obviously have to be a pre amp output of the head unit. Does antbody know the standard head unit output Volts for the amps. The standard head unit is crap and want to put in a alpine or Blaupunkt head unit.