The only thing that would make any sense is if the Apple TV changed the format of the stream it is presenting to the Kanex...or the Kanex has broken. The Apple TV needs to be locked down to Dolby Digital in its audio settings. Anything more than that could be sent to the Kanex, but wouldn’t be sent across that optical line.

Yes, there is a minuscule possibility that the Beam or adapter is broken, you’d need to submit a diagnostic for the Sonos folks to look at the electronics on the Beam, but that is , as I say, minuscule, compared to the audio settings on the Apple TV.