01 Denali w/ Bose Luxury problem

I just purchased an 01 GMC Denali with the Bose luxury system(Y91 option). I have no sound at all 4 door speakers. I do have sound at speakers in the console and the speakers at the rear doors and the sub. But nothing at all in the 4 door speakers. Would I look at the head unit or the amp for this problem. I do get an anoying buzz at a small speaker in the headliner, even if unit is off. On star seems to be working fine if thats even related. I'm lost and looking for some direction. Thank you.

Start by checking the amp as it might have blown causing the 4 speakers to cut out. As for the speaker in the headliner having the buzzing sound it sounds like that speaker has blown out on you.

Thanks for the reply , Dave but I just got a known good amp from the salvage yard at the tune of 175 bucks. Same thing, so I think I eliminated the amp. Thats what I thought it was at first too. Unless theres another amp somewhere i dont know about. I found this one in the rear quarter panel. Must have more to do with the radio itself. I just didnt want to keep replacing expensive components if I didnt need to. Thanks again for the reply.