Likely that the source material is encoded in that format. You need to make sure that whatever is being watched on the TV is being sent properly, sometimes that means being particular about what your watching, sometimes that means adjusting the audio settings on the device sending the signal. 

That TV model was released in 2013. More than likely, it cannot pass through multichannel audio from external media devices connected to HDMI. You might possibly be able to get Dolby Digital 5.1 audio from the TV’s native VUDU app or by playing 5.1 videos from a USB drive connected to your TV.

You should consider getting the HDFury Arcana eARC adapter so your external media devices can bypass your TV’s limitations and send audio directly to the Arc. I use the Arcana with my 2013 plasma TV and Arc and it works great. Because of the Arcana, I can get 5.1 and Dolby Atmos audio from my Apple TV 4K, Roku Ultra, and Panasonic Blu-ray player.

Thanks GuitarSuperstar.

I’ll try that.