I have the Sirius antenna on top of my truck, how do I plug in to that!?!

I have the Sirius antenna on top of my truck, how do I plug in to that!?

I have the pre-wire hook-up on my '06 F-150. But I have an aftermarket dvd player it's a kenwood. Right now I have Sirius in my truck but I had to put an antenna on top of the truck. It just looks stupid with one from the factory from ford, and the aftermarket antenna on top of the truck too. So I have two antennas on my truck roof. How do I plug my aftermarket piece into the ford installed antenna. So I only have one antenna on my roof???????????????????

I'm not sure how to do that, the only thing i can tell you is to put your sirius Antenna on the dash, thats what i do because its bad enough I have a On-star and XM Antenna so I have 2 antenna for 2 services I dont Use!! If you put it on the dash, make sure its not too close to the window and reception is good for being inside the car