I bet they used an FM mod to connect you unit. The other thing it could be is the antenna could be in the wrong area. You want to make sure that it's on the rear end of the car on the outside too. That's key.

My experience with Circuit City is they're a bunch of monkeys. Usually they don't seem to know what they're doing. My suggestion would be take it to a Tweeter is one is around your area. Tell them that you want you XM hardwired into you radio. They'll add a direct FM mod that will connect straight to your cars factory antenna jack. It's the best and only way to do it and it's only about $25 or so.

Good luck, let us know how it goes.