Factory audio system problem

Hello!
I just joined this forum today and would like some ideas on a problem with the factory audio in my 2000 Yukon. Seems that suddenly the sound quit. My factory system in not the Bose one, but has 4 in-door speakers and a "sub" in the rear bay on the driver's side. The head unit (CD version) operates just fine (plays CDs, tuner works, etc.) but no sound, no hiss, no static - nothing. I checked fuses. I pulled the unit out and checked connections. I also located what I think is the amp behind the glove box but could not figure out how to pull it. I got the top clip off holding the unit to the mounting bracket, but that's it. Anyway, is this a typical problem (sound quits)? If it is the head unit, I'd just as soon replace it with aftermarket and just use the factory amp for now. Problem is, I can't tell if the head unit or the amp is bad. Any help would be appreciated.
Thanks!

Hey, this is the 2007+ section, you'll probably have better luck in the 2000 section.

sorry about that. Will do. Thanks!

that silver box behind the gole box you are talking about is the XM tuner. Ay least that is where my XM tuner is on my 2007 Denali and my 2004 Denali that was also where my XM tuner is. So if you have XM radio I am sure that's probaly the XM tuner