4 years ago I installed a 6 CDs changer in my wife's car via an FM modulator directly connected to the antena input in the back of the factory radio. It has been working well since and the sounds is surprisingly very good. I do not hear any difference between a CD played in the changer and a CD played in the factory installed cd player. The trick was to adjust it to the right FM frequency. I would not recommand any FM modulator based solution where there is no hard connection between the transmitter and the receiver.