If both the TV and Panasonic HTS have ARC over HDMI then the HTS needs to be connected to the TV HDMI-ARC input. ARC has to be turned on in the TV menu and selected as you source in the HTS.
If they don't then you would need to connect the audio output of the TV to the HTS. Most likely connection would be optical audio. If you don't have the corresponding input on the HTS you would need a converter.