Glad you mention this. I have not received the update yet (11 months and 4 days with the problem, but who's counting?" But for months now, durring the time the radio plays before it times out it doesn't sound right. Most of the sound comes out of the front 2 speakers when the mixing control is in the center. I have to put the mix control most of the way to the back to get all the speakers to play and then the sound is very muted and doesn't sound good at all. I was hoping the OTA update would fix this, but your post makes me think it may not. The other symptom I have is zero bass out of the sub woofer. Adjusting the bass up or down has no effect on bass at all. I remember when we first got the Compass the radio sounded really great, at least until the volume went away. No it doesn't sound right at all.
Your description of "muted" is a good description of what mine sounds like too. I get the feeling that the OTA may be only the start of trying to get the radio fixed.