It's not possible sorry. You can only select one output source.
If you send the sound to the headset, then you can't also send it to the HDMI or digital optical output to the TV.
If you want the headset just for voice chat you need a PS3 type headset that has a mixamp, so you can connect the headset to the PS4 via USB and use it only for chat while the sound is going to the TV. That is your best bet i guess.
But as you are asking it wont work that way! there is no possibility!