Something wrong?

I have a 98 Tahoe with a alpine cda 9827 cd/mp3 player and today I bought new door speakers infinity capa perfects 61/2 well I hooked them up and everything works perfect with the radio on and then when i switch over to the cd player the front speakers work and the rear doors have nothing. My truck has 6speakers in it the 4 61/2s and then 2 4x10s in the rear roof. I dont know whats wrong and ive checked the wireing on the speakers and its fine its just when the cd player is on the front door speakers work and so do the rear roof just not the rear doors. What could be wrong.