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.