Don't. 

Seriously, don't as the Era line is not designed to connect to a TV and you will have delayed sound  / lip-sync issues. Use a Sonos soundbar or Amp that are designed for that.

If you must the audio input dongle for the Era hooked to the analog output of the TV will be as good as anything. 

And, to add to that advice, Sonos isn’t made to connect directly to set top boxes. Their soundbars are designed to connect to TV sets.