i pod help

I have a 2003 supra launch. The deck is a kenwood. Behind the deck are two sets of red and white imput cables hanging loosely. I can plug in my ipod to these inputs. When i plug it into one set it plays out of the front speakers and when i plug it into another set it plays out of the back speakers. I have to have the radio on at low volume and the ipod on high volume to hear anything. I was thinking that i could get a splitter and another monster cable to make the music come out of both sets of speakers, but there has to be an easier way to do this. Any help is appreciated.