PS2

I hooked up a PS2 in my buddies car yesterday and the sound only comes from his front speakers. Hes got a pioneer premier deck, it has 3 sets of RCA's on the back, one is labelled rear output and is on wires and the other 2 sets are mounted to the back. His amp is hooked up to one of the solid mounted ones, and teh other is labelled output so i put the ps2 audio into the other set and it works but only front speakers? And theres no seperate mode for it, you have to pause the cd. Anyone know how to hook this up so all speakers work?