Spoke to dealership, he said replacing the amp won't solve this problem. The issue of the buzzing of the speakers with the car off and distorted audio at high volume is related to the tsb below where they need to reprogram and update the software related to the audio, now I have to decide whether to get this done for $250 or find an alternate way to resolve this issue.
https://bmw-worldzz.blogspot.com/201...sound.html?m=1