Bazooka make a set up that plugs right in, if you don't mind spending the money. Here's the lowest priced one I've found so far. Yes, I'm looking too, just can't hear it at highway speeds. Sorry, this one is just the amp and wire kit.
[ame=http://www.amazon.com/Bazooka-MC-YAM-AMK-Yamaha-4-Channel-Amplifier/dp/B001MJ0GZC]Amazon.com: Bazooka MC-YAM-AMK Yamaha 4-Channel Amplifier Kit: Car Electronics@@AMEPARAM@@http://ecx.images-amazon.com/images/I/51c8ToZr0TL.@@AMEPARAM@@51c8ToZr0TL[/ame]