If they do get a court date, get a lawyer. They're expert witness is a moron and could be completely debunked by any competent Electrical/Electronic Engineer. Hell, just mentioning that the audio shop guy managed to "rewrite Kirchoff's Law" would go a long way. Also with a lawyer, you can sue for your time and troubles. That and do the things that G Rahn mentioned.

I had a buddy that put an aftermarket DVD/Nav head unit in his car. He had to go and get an alternator replaced that went bad. The dealership told him the same thing. Not covered under warranty because the DVD unit caused the problem. Both being engineers we went back together to hear this one.

According to them, the stock 150 amp alternator, that is also used to supply fully loaded Chrysler Town and Country minivans with full DVD systems, a slew of monitors and such went bad because the alternator was not designed to power an aftermarket head unit. After grilling them, they "decided" to let it slide this time.