I understand you want what you want. But in case JRiver does not accommodate you, you can still solve your problem.
I don't think the TV has a headphone jack, nor would I want to be tethered. Also, occasionally I'm not alone, so that couldn't work.
First, if your TV sound goes to a receiver, you can plug headphones into the receiver.
Second, all (reasonably modern) TVs have an audio out. It may not have a separate headphone jack, but the existing audio out can be used with a splitter, so that sound can still go to your receiver or soundbar while being also sent to the headphones.
And you need not be tethered. There are plenty of wireless options available, and some of them support multiple sets of headphones simultaneously. Here is one:
https://www.amazon.com/Avantree-Bluetooth-Transmitter-Receiver-Simultaneously/dp/B07BQYYDNJAvantree even has a unit (the Orbit) that decodes Dolby Digital, so it will work with the Netflix app on your smarttv, without having to output as PCM.
Here are some more units:
https://www.headphonesty.com/2019/10/best-bluetooth-audio-transmitters-tv/Plus, I enjoy listening to action movies LOUD, but the person most likely to join me doesn't like it as loud, so even if we could pair both our headphones to the TV directly (not sure it's possible), we'd have to settle on the 'right' volume, which wouldn't please all parties.
Not really a valid complaint against headphones, as you have that problem now with your speakers. Speakers in a room play at one volume level, not two.
An easy way to address this is just get yourself bluetooth headphones with their own volume controls. Or, use a splitter with volume controls. They exist, cheap. Google will show you. Either way, you get multiple headphones with independent volume controls.
So yes, you can hook up multiple sets of wireless headphones to your existing TV, each with their own independent volume controls.
Hope this helps. Good luck...