I had a similar problem. I have the standard audio however.
I went out with some friends to a resteraunt, and when i came out i started the car there was no sound whatsoever (no am, fm, ipod). There was no hissing or humming coming from the speakers, it was just dead quite. It was a very bizarre experiance. I muted and unmuted the radio, and it did nothing. I shut off the car and restared, adn still nothing. I drove for about 5 miles turned off the car and restarted and stil no sound. Then I drove about another 5 miles to a friends house, went out to the car after about an hour or hour and a half, started the car and it worked fine. Any idea what this problem was. It happened about 2 weeks ago. I have owned the car since august without a single problema and the car has 3600 miles on it.