the car is prewired for the BMW sirius reciever
xm makes a translator for the XM direct box to hook into that as well...

the decision is personal prefrence based
Sirius has better selecitons of punk, rap, Mashups, dj mixes, techno
XM is more geared to the middle aged set

also sirius gets nascar(for those that like it) from xm for this season

the box goes down by the battery in the 4.6 you need to get the extenstion cable that runs over from the CD changer to hook it up

also check the part number on the FM tuner (silver box in battery area with becker label on it) to make sure it is a sirius enabeled tuner otherwise you need to get a new one.