I've posted about it elsewhere. But essentially the way they have it set up is there are two main modules of concern in the audio system: The ACM which handles all audio routing, volume controls, radio and sirius tuners. The APIM mostly just handles the bluetooth, USB, aux inputs, and nav. The APIM merely feeds the audio to the ACM for output and sends commands to it for stuff like volume, tuning radio/sirius, etc.. What is essentially happening is the ACM is freezing/locking up and the APIM is no longer able to communicate with it which accounts for the symptoms most people see. For once this is a scenario that Sync is not the issue.
EDIT: Should also add there is the ANC (Active Noise Cancellation) module in the mix. The ACM sends audio through that which then takes input from the microphones, mixes them in, and goes out to the speakers. Though outside of the usual reported issues of odd noises, there haven't been any major showstopping bugs here. One side note if you check out the wiring diagrams the center speaker bypasses the ANC module and comes straight from the ACM. This explains why if you end up restarting the car or going from Accessory to Run, the center speaker is the only speaker active for a moment.