You want the one that isn't designed for factory amps. The Ford radio system uses an internal amp in the head unit to drive the speakers. The option that Soundgate is referring to for factory amplifier systems are systems where the head unit produces a very small (line level) signal that goes to a factory amplifier somewhere else within the vehicle and you're taping the signal on the way to that amp. Since those line level signal are very low, they take a special converter that is more sensitive. That kind of system is more common in the high-end Lexus and GM (Delco / Bose) systems.