sub with sony 6cd

[cdo1uk]

I have a focus 2005 MK2 with a sony 6cd player in it. the sound is pretty good, but would like to add a sub and amp and leave the head unit running the Speakers. how can i do this without taking off the rear Speakers and running a high level input to the amp for the sub?

I would like to keep the front and rear sound and add a sub.... or will i have to just changet he head unit too?

thanks

[Slugsy]

only way you can do it is to run speaker to rca converters on each rear channel run one for the sub and the other into another amp to run the rear Speakers and amp the rears