406 radio upgrade

Hi, I have just upgraded my standard 406 coupe radio (mfr'd by Philips) with a Pioneer CD player. The car came with the JBL amp/speaker system which was in the car from new. I've put the new Pioneer in the car, fitted the standard ISO cables to the back of the radio, but I can't seem to get any audio out of it. The new radio has pre-outs, but there's no generic RCA cable, that I can see, that runs to the amp in the boot. I'm assuming then that the ISO connectors (the speaker one especially) either isn't a standard wiring layout, or there's some other method the Philips radio used to get the audio to the boot that I either haven't got a connector for on the Pioneer, or I'm missing something. Has anyone tried this, or know of a way to get around this and get the audio to the amp? Regards, Dan