Aftermarket heading and factory satellite radio antenna

[TheBoss]

Is it possible to use the factory satellite radio antenna when using an aftermarket head unit with a built in satellite tuner? The guy at crutchfield said the alpine I'm looking at uses a special antenna because it's looking for either Sirius or xm instead of a Sirius only or xm only signal. Make any sense? I really don't want to run an aftermarket sat antenna.