How to get Headphones and TV speakers to work simultaneously

[chellmer]

I have headphones that have RF plugs for the charging base.  I have purchased a converter box that plugs into the eArc HDMI port and I am only able to get these to work as the primary audio source when on.  I have gone into my audio settings and set HDMI eArc to Auto.  

How can I get these to work without affecting the TV speakers so they are both the headphones and the TV speakers are working simultaneously?

[270]

Why would you want to do that?

[chellmer]

My Mother in law is hard of hearing and prefers to use headphones..while I would like to hear volume through the TV speakers at the same time.