car speakers help!

im using a sony cdx-L450 car stereo for my car, and my car has no rear speakers built in. I already have a pair of 6x9s for the parcel shelf of my old car, so im gonna use them.
pulled out the cd player and see how to connect the speakers, and see a load of wires, and then two phono sockets one red one white with labels saying 'rear left' and 'rear right'.
i assume these are the rear speaker connections so buy some phono cables, route them through my car and plug into my speakers.
so all is plugged in and when i turn on the cd player nothing comes out. i set the fader to only play through the bacl speakers, and i can just about hear the radio on full volume.
anyone know whats wrong? am i using the right connections here?
really appreciate any help, thanks!