Best answer by Airgetlam
Generally speaking, in many TV's, there's a setting to turn on the digital output.
You don't have a Sonos device that requires an HDMI cable. You have one that requires an optical cable. The optical cable that came with the PLAYBAR would be connected to the output on the back of your TV, and the input on the PLAYBAR.
When the digital output is on on the TV, there should be a red light coming out of the optical cable, before you plug it in to the PLAYBAR.
Here's the FAQ: