hc361
I have an option in the TV settings to enable headphone and TV speakers 'on' simultaneously. The headset also has its own volume control as well as a 'slider' on one of the cans. Does take a small amount of time to set up at first, but works well.
murraymints
My sets now obsolete!!! Closest match are these at Amazon
http://www.amazon.co.uk/gp/product/B003X5TZPA?keywords=Panasonic%20RF%20wireless%20headphones%20%28RP-WF950H%29&qid=1456071456&ref_=sr_1_1&sr=8-1
I'm not saying buy them at Amazon, because I bought mine elsewhere.
Suggest you check the TV first to find out if there is a setting to output sound both to headphones and speakers.
Another option was to get a headphone that can connect to the audio out sockets on the TV. I believe that Sony had some that could connect in this way.