Add factory GM XM radio

Where do I get the unit to add XM to a friends 2004 Chevy pickup, with the steering wheel controls that works with the factory head unit.  I saw this on another friends GMC and he had a pioneer antenna, but all the XM worked thru the factory radio and steering wheel controls.

Do I need to get a factory XM unit and add a aftermarket antenna?  Is the factory the 2 plug or the 1 plug?

Thanks

yes, it can be done look up a company called terk. Your looking for XM Direct