The cleanest way to do it is to add an iSimple gateway. Your radio is capable of XM radio which is required to install one of the iSimple gateways. Your "band" button is how you'd toggle through the different sources. Basically, you hook up the "gateway" with a car specific harness. It plugs into your stock radio harness, plugs into the gateway and also plugs into your radio.
They make a few kits depending on what you want. If you are just after aux inputs, those kits are the cheapest. you can get one for as low as $65. If you want iPod/iphone and aux input, those kits sell for around $100. eBay is your best bet for finding the cheapest price. simply go the iSimple website and put in your car info. It will tell you which kits are compatible with your car. Search the kit model number on eBay.
I have had one in my car for several years now with no problems. Installation is a breeze. If you opt for the iPod/iphone gateway, it will also show song text on your radio. also, you're able to cycle through songs with the head unit and steering wheel controls. It basically tricks your radio into thinking there is a factory XM receiver installed. I also have an aftermarket XM receiver installed in my trunk that hooks into the gateway.
both make these kits and I think they are the same company to be honest.