I'm having the same problem with my 06 Pacifica. It has the 6d DVD/cd/cass/Sirius.
I've posted this on the Pacifica forum and it seem that a lot of people have this problem.
On the Jeep forum there's a refrence to a RB1 adatper cable to hook up between the Sirius and the Radio(RBP) with Nav.
look at this forum and see if this might help you.
I'm going to the dealer friday and see if they know anything about it.
Pacifica forum about Sirius
"The adapter is part #802208322 RB1 adapter for vehicles with an RB1 navigation radio and cd changer.