Dutchie,
It must be different with the NAV radio. My guy has the right antenna adaptors. So he has the correct antennas plugged into the FM modulator. He thinks that the modulator is cutting out some pre-amp signal for the car antenna, so the signal is too low after it comes out of the modulator.

One of my problems is I am relying on the installer. I have not seen the back of the radio.

Thanks