I went to Best buy to buy an adapter between 4 k Tcl and older Panasonic home theater. I was told that 4k audio speaks a different language that anything oldedr and no 4 k. Is this really true and do some adapters work???
Your problem has nothing to do with 4k.
Your HTS doesn't have HDMI-ARC so you can't use the HDMI cable that plays the DVD on the TV to get sound from the TV to the HTS. ARC only works when both the TV and HTS have it and both are configured correctly.
The HTS only has analog audio inputs so you can connect the headphone out of the TV to the HTS. You just need a cable with a stereo 3.5mm plug at the TV end a 2 RCA plugs at the HTS end. Select a surround mode like Dolby Prologic that is designed for a stereo input. Not digital surround but no way around this without getting a new HTS.
I went to Best Buy to buy a cable Tv headphones out to Rac fittings. They had one but the sales person told me it will not work. I came
home looked online Amazon got a Kaposev digital to digital/ analog around $25 with short opitical av. Hooked it up had to change optical av port to 2nd one works perfect. Thank you for our help 888