Wait until you have to deal with there cust service.
I had 2 receivers. 1 in my wifes car, 1 that i moved between my Jetta and the truck. In June we replace the wifes car with a new VW (diesel) that has sirius built in. I kept both receivers, one in the truck and 2 in the jetta.
They started emailing me that the 1 receiver subscription was about to expire (and they were ready to automatically charge my credit card) so I called them, explained my Jetta got totaled and to let the subscription expire. They ended up canceling the subscription and charging me $75. 00 early termination fee! after a pretty nasty call they gave me the $75. 00 back (they wanted to credit my account).
The receiver I have in my truck was to expire Dec 31. Back in oct I ordered a new truck with sirius built in so I called them and told them to let it expire. Around Dec 23 I Called them to extend the receiver for 3 months because the truck is not here yet. They took the money and said "thanks".
Dec 31 the receiver shutoff! I called, they had applied that payment to extend my wifes receiver (that don't expire until June). All said and done, they fixed it.
Note: If you have 2 receivers, you will have a "main" at full price and a "secondary" at the discount. If you let your main expire, and your paid up on the secondary they can't charge you additional money to make the secondary a main! so just before you main expires, update your secondary for a year and your set!