Well isn't this just a find how do you do!!
It appears that on this set there is no headset or other audio connection other then the optical?
It appears the only way to a traditional RCA audio jack is via a special adapter. See image. Inexpensive not sure of the quality of audio.
The best way would be to purchase a sourround sound speaker amp system with 5 speakers plus base woofer. These surround sound systems are usually have optical connected and for best results this would be my first choice.
Some have wireless back speakers to allow for easier installation.
RCA RT2781BE 1000W Home Theater System with Bluetooth
This unit has two optical inputs and one digital input.
This is an inexpensive surround sound speaker system that should connect to your Panasonic TV optical output. Very available and I wanted to give you at least one option. Wires etc are a mess but the surround sound can be amazing. I would check all the reviews if you decide to go with this type of audio system. They can be confusing and in your case you need to have input control of volume with optical.
The following link is the manual for this particular Home theater System.
These audio systems can be very expensive. Less expenesive sorround can still provide great listening results.
Hope this helps?