I have just fitted the UAD system to my 2012 RR, I had an awful sound quality.

There was very little on any forum to help, however the issue has been found and I thought I would share the fix.

The issue is that the UAD unit is providing too much audio output to the Car. You need to turn the phone to Aeroplane mode so that Android Auto stops working, the RR screen will then show the home page for the UAD system. Go to settings and you will find volume settings for all the possible outputs. Reduce these from 100% to 50% and the problem is fixed. Glorious high quality sound.

hope this helps someone in the future.