Another option is to skip the unit entirely and just stream SiriusXM through your phone into an aux jack or through a Bluetooth receiver. If you are without cell coverage many times or don't want to run up the data charges, I get it but just offering a much lower effort way to use the service.
The unit installed in my 2006 M35 is a very old receiver and can only get the original number of channels. The newer receivers can do many more channels. Not all the channels below 100 are available on the older boxes, it just depends on where in the spectrum the channel actually sits. This older unit also sounds like doodoo compared to newer units. Now that I'm using Spotify to play music more often in the car, my old satellite radio stations are almost unbearable to listen to. My antenna is slightly broken so any trees block all signal but since it's a digital stream, you either get it or you don't so there's really no effect on quality from the antenna.