https://www.ebay.com/itm/2-In-1-Blu...740906?hash=item2acab8e36a:g:c18AAOSwo61cxA5J Optical to bluetooth transmitter adapter.
This 1 in 2 Out Digital Toslink Fiber Audio Optical Splitter Cable is specifically designed to split a single signal into two, allowing you to connect multiple devices. TThe 1 to 2 TosLink / Optical audio splitter adapter is ideal for connecting your CD player, DVD player, or other digital audio...
www.ebay.com
Optical splitter, sometimes it requires an actual switch box, the switch boxes are $30, but I think a splitter in your case would be fine as you're not trying to pair multiple devices to one receiver (ie, plug a DVD player, bluray, and the TV into the receiver) you're simply wanting to make the light signal from the TV go to two things at once. If you run two different light signals they'll cross and not work, though.
EDIT:
You might be able to get away without the splitter with that bluetooth DAC box, as it says optical in/out on it, but I'd buy the splitter to be safe.
So yeah, with the $30 DAC bluetooth thing from China, you'd get a 3.5mm headphone jack output and bluetooth. So one split optical signal to sound bar, one to DAC. DAC transmits bluetooth to bluetooth headphones, hopefully no audio sync issues happen (who knows?) if they do, you need wired headphones.
For a subwoofer you could use the 3.5mm split into two with a 3.5mm female Y adapter,
https://www.ebay.com/itm/3-5mm-Ster...470299?hash=item46724eb05b:g:h9EAAOSwFsBdFQST Like that, then you'd have two headphone jacks plugged into one port.
Subwoofers use RCA usually, unless they're proprietary to a brand/all in one setup, so you'd need a 3.5mm to RCA cord like this
https://www.ebay.com/itm/5ft-1-8-3-...095298?hash=item2f3afc9782:g:NXIAAOSwvthfmOAB
Then you would plug that into the subwoofer and ideally use another Y to put it into the generally one RCA input of the sub.
https://www.ebay.com/itm/RCA-Audio-...406665?hash=item48cb4c1689:g:CLgAAOSwAj9dl5Ir But if the sub happens to have two, then you don't need this.
With this setup you could use any random home theater sub of almost any brand as long as it has the RCA input, and find one very cheap off Craigslist or at a thrift store (I have a 100w Sony home theater sub I paid $15 for off Facebook Market...) I think your soundbar is meant to use its own proprietary sub of some sort, though, with its terminal setup.
For quite a few years I did a similar setup but not with headphones, I'd use a 3.5mm headphone to RCA cord from my computer to a Panasonic all in one stereo, then I separately Y'd off to a powered subwoofer with RCA input later on. Now I have a much better stereo receiver and speakers with its own subwoofer out on the receiver, but I still use the Panasonic in my garage as a stereo still with the same RCA to 3.5mm cord to play my phone.
It's about $50 into adapters there, but I think it would allow you to do exactly what you wanted. Also, though new you'd be paying a pretty penny, people are practically (or sometimes completely) just giving away older and newer surround sound receivers now. A surround receiver with only optical and no HDMI usually only goes for $20-50 now, but even some fairly modern ones with bluetooth out aren't going for a lot. People are also practically giving away OK speakers, too. I built my downstairs surround sound setup for about $100 in, including receiver, front and rear speakers, a center speaker, and a sub, just from snatching up deals on Craigslist and Facebook over a few months, using an older early 2000s Denon receiver with only optical in. Of course if space/etc is an issue, then keep with the soundbar, but the prices nowadays on the used market are insanely good. With a receiver you could just use the headphones (since the receiver has buttons to turn the speakers on/off) with a bluetooth transmitter and you'd be done and have it all in a somewhat convenient manner.