My wife's new Honda Pilot includes a nice built In XM Radio. We're going to buy a 3 year XM Sub for it, (the length of her lease), and would like to add the Best of Sirius to the Sub. If we pre-pay 3 years for the XM Sub, how is The Best Of Sirius handled? Is that done month to month? Or, if can we also purchase that for 3 years upfront and hopefully get a discount. Thanks!