That sound like an amp problem, especially if it threw a code for it.
I have no sound in mine neither, but my sound just stoped from one day to another, everything works eaven the mic for the BT but I get no sound at all. I have tried to update the SW thru
www.bmw.com/update and have replaced the amp with no result.
So I have an amp over, but I live in Sweden so I think it's easier to source one locally for you, a new one is about 1300$ i think.