I've spoken to tech support about this over a year ago, but see no progress in correcting the problem.
When selecting ALL channels in SiriusXM, Sonos only shows those channels in your library within your Siriusxm account, and even that list is not 100% accurate.
When selecting ALL channels, you should see a list of ALL SiriusXM channels, as you see when logged into the Siriusxm app.

