You won't get 110.8 on the SL-40. However, rather than spend another $2k for the SL-30 just for the occasional ATIS why not pick up a used 396/496 with XM (including METARS). This would give much more capability plus money left over.
That would not help you any if there is a GPS outage like the upcoming ones in the Florida and Georgia area.
Would the GPS outage affect XM? I think these are two different satellite systems.