Speakers not working/Corded headsets do

An object hit my factory installed rear radio (2003 Yukon). The car stereo (factory installed radio with 6 disc CD) was playing a CD at the time. Minutes later, the car speakers went dead. For an hour the car speakers worked intermitenly, now they are out completly. I can plug in a head set to the rear audio and have sound through the headset. Although only 1 of the 2 headset jacks work. I've tired every button. Any ideas? Or any recommendations on who/what type of service center should I take the vehicle to?