no interior sound

If you have a speaker laying around the house, use it to test the channels on the cd player, Pull the cd player out and hook the speaker up directly to the back of the radio, sounds like the internal amp is gone.

 i have a kenwood kdc-x615 cd player in a 92 deville, i got locked up and came home a month later to find that my interior speakers no longer worked. the cd player works fine just no sound. i hooked up my pre amps to my brothers set up and it worked perfectly. he said it might be the interior amplifier inside the cd player. how would i check this, and if thats not the problem what else might it be?

i tried hooking up a different speaker and it worked so its not the internal amp, its something inbetween the head unit and the speakers, its not possible all the speakers are blown, they would still make some kind of noise wouldn't they? im really stuck on this