It can't recognize it. With a Sony Changer you have two sets of wires connecting it. The wire that controls the changer and the RCAs that send the music. If there is no changer connected, you will not be able to select the changer option. It might be interesting to get a changer and have some type of switch on the RCAs between the HU and the changer though. You might be able to fake the HU into believing the changer is sending the signal...although, it would prbably be easier and cheaper to get an FM modulator.
