sorry guys, i think this is a very techy question. if your car cla does not come with a siris radio receiver, does the existing antenna support the addition of siris. dont know if im putting it succinctly or not. my cla will not have the siris radio receiver, but i have an add on siris radio that i plan to put in my cla. can i use the existing cars antenna or will i have to use the surface mounted magnetic one that comes with the add on?? i know, i know. i have not put this well and it is a tough question. all help is appreciated.