Called Polk. They do not sell the motherboard. if under warranty, they will have Massimo send you a new soundbar and won't even ask for the old one to be shipped back! if not under warranty, then congratulations, you now have a very expensive anchor which can be attached to a chain and thrown overboard to stop your small boat from moving while fishing.

The motherboard is a very easy part to replace. a few screws, a few plugs and a ribbon cable. But Polk won's sell them to you. Don't purchase Polk products unless you want a product that has no viable repair options.