Well, I was annoied by this once too, then I bought the empeg.

But, I wanted to hook a mp3 player up to my sony headunit once and started to
dig out all the info I could find on the unilink. (Even fried a $800 Sony head unit to dead..) After buying the Empeg I gave up on the whole thing, I did turn over my findings to another guys who mailed me about the same thing.

There is now a working PIC microntroller which will let you enable the AUX input of your sony headunit + other small programs that can run on a PC too..

Have a look here, follow the link. http://www.eriksen.no, you will find what Sony didn't want you to find...

PS. Sony does have a unit that allows yout to enable the AUX input, can't remember what it is called though..

TommyE