Pioneer!!! AUX IN HELP!

i have a pioneer deck, its the model below the MP3 capable... my question is i have the audio jacks that are hooked to my subs, and im looking to put a lil mp3 player to it, now i bought audio cables with a headphone jack on them and i plug it in and it doesnt work... now my question is that those must be for subs, on the back of the deck is also a headphone jack.... do i buy a double ended headphone jack and use AUX in will that work? anyone know?