I have a question about the Shaker 500/1000 audio systems in the 2006 Mustang. What is the difference between the two, and is the Shaker 1000 worth the additional $1000? I DO like to listen to my Jimmy Buffett cd's when I'm driving to work, and I want something that won't disappoint me in terms of sound quality. Is the Shaker 1000 worth the additional cost?