Swing cd

Hi all, i have done several searches but cannot find the answer so....

I have a 59plate FL Octavia "S" fitted with a "Swing" single cd/mp3 player. I want to be able to add an MP3 player with the help of the lead i used in my 06 plate octavia with a Stream cd. After looking at info online i have viewed that i need to change the placement of a few wires but will still fit into my new cd player. The question is, how do i activate the Aux in (pretending to be cd changer)? On my Stream cd i pressed the cd button twice. Will it auto sense the lead and give me the option to switch on?

Hope i have described what i want to do....

Thanks in advance

Kyle