I CAN say, don't go with 2 Wheel Tunes. They went out of business and no longer support their warranty and don't even make replacement parts. Problem is, there are still a LOT of vendors out there with a lot of these systems in inventory... and they will sell them to you without filling you in on the current state of the product.
I went with
www.cyclesounds.com. Everything that WAS 2 Wheel Tunes is now at cycle sounds. It's a small and unobtrusive system with quality sound. Only problem is, it doesn't actually include a radio. It's just the sound system. But you can plug in just about anything. iPod, XM, Sirius, whatever...