I am wanting to put an aftermarket DVD player in my 2004 GMC Sierra 1500 ext cab. I have factory onstar and xm and want to keep both. I know that I have to get an adapter like this http://www.logjamelectronics.com/pacos2.html in order for it to work. What can I get to in order to retain the factory XM radio? I also have settering wheel controls. I know for the steering wheel controls I have to get a PAC unit in order for them to work.