If they are then they really don't have a clue what they are doing !!!
In this instance i agree with Ganzoom 8k for a head unit is an absurd amount, even including labour.
If i was the dealership i think i would be trying to get hold of another car with the same sound system (looks like ML) and then trying an exchange between the cars, if it's proven that it's the head unit then they can just order a new one under warranty.