So all you can use then is the antenna? purchase the aftermarket tuner connect the factory antenna?

 

It has already been answered and it is NO. EVEN if you had Sirius in the vehicle before and bought a sat-ready head unit, you will still need the adapting unit for the specific head unit. In essence, your factory installed Sirius will be a non functional hoodus that lingers on the vehicle once you remove the factory unit.
Each company (JVC, Pioneer, etc) has a specific adaption for Sirius to work. Average price is about $100 for that sat box.