It is most likely that the HDMI connections on your TV are inputs, not outputs.
Do you have audio outputs on the TV (digital coax or optical) or even RCA that you can connect to your headphones?
You are right! The TV manual shows HDMI In slots.
Yes, the TV has audio outputs but the headphones will not fit in the hole. I was told that digital sound could not be hooked to analog headphones; thus the reason for conversion. Probably why there is no headphone outlet on newer TVs.
Thanks for answering.