This may have been mentioned before, but a quick search didn’t find anything.
Note first that I’m still running S1. (I know, lucky me.) It’s possible that the same will apply to S2.
Starting a few weeks ago, I noticed that many of the SXM stations I had added to my SONOS Favorites were no longer displaying cover art and song/artist/album info. Oh, well, at least the music was still playing.
This morning I happened to select one of my SXM SONOS Favorites directly from the SXM “Browse” interface, and suddenly the missing info was displayed. Switched back to the Favorites selection; still missing there. So I deleted all of the SXM stations from my SONOS Favorites list and re-added them, and now I know who’s singing.