I am trying to figure out who is telling the truth if any. I want to put my alpine stereo in my mustang that has the mach 460 system, but a guy at circut city said that the stock amps for the rear speakers will not work if i do this. Then he told me I need to buy a $40 wiring harness (ford premium wire harness) and a AM/FM antenna for $15 to get FM with my aftermarket alpine unit, and the installation unit so my alpine will fit. Do i need all this stuff or is it BS let me know