Trying to get bluetooth headphones connected for TV audio

Couple of good things to try.  THANK YOU!!  I'll report back if that works.

It looks like most smart TVs now have BT transmit built in, so you can turn speakers on/off.  Yours sounds older than 7 years so it will be much harder to do. 

Can you hook up the bar to the headphone audio?

Then you could y-cord to a BT transmitter or wired headphones (if the latency is unacceptable.). Then turn down (mute) the bar during headphone use.

you should be able to use your phone as a remote with a Roku device.  If you haven't already, download the Roku app and pair your bluetooth headphones to your phone.  You should now be able to hear your headphones as long as they are "paired" in the app.

I am not familiar with your TV, but the TV's menu (under audio) should have the option to connect to your headphones without any latency issues.  All my TV's have that, although I don't use it.