I lost the sound on my discovery nav pro mib1, nothing seemed to bring it back (tried soft and hard resets), the sw version it was on was 0290, I had it booked into VW who couldnt see me for two weeks and driving round in silence was driving me insane! I managed to find a copy of 0388 on a German forum and updated it myself.
Since then I have had no issues, would be good to get my hand on the latest version if possible but suspect would have to go through VW!