The devil is in the details, which seem to be missing.
Polk makes several soundbars. ...and Yamaha makes many different receivers. Exactly which ones you have might help us help you better. As it stands, I can only offer generalities.
Does the receiver have an optical analog output? I know they have inputs but I'm not to sure about inputs. But, there's a lot I don't know, too.
But, for starters, try using red/white analog interconnects (which at least one Polk model says is included) from the TV's audio outputs to the soundbar.
Or, if your receiver has an analog output, you could run that to the soundbar, but don't these have their own amplification system built in, making the receiver redundant?