cd changer rear input Aerio 2005

[alganis]

I want to add an MP3 aux jack through the round multi pin cd changer input located at the back of the OEM stereo.

I read in the manual that pressing the CD button once turns on the in-dash cd, and pressing it twice (double click ) turns on the external optional (trunck) cd changer.

My question : can I hock up a cable to the back of my stereo through the round multi pin input to serve as an AUX input to connect my MP3?

I don''t want to use an FM addapter as my antena is already occupied with an FM modulator for an external satelite radio.

another question : does any body know how many pins in that external cd changer input?