New Samsung TV, can't use headphones and speakers at the same time

Yep. Minimal information to begin with. No acknowledgement of suggestions. The only “thank you” in the topic comes from a third party who found some piece of information useful. I think we can say this topic is done.

Btw, I have a sneaking suspicion that some Samsung tvs have Bluetooth radios but Bluetooth is disabled in firmware. You can get into the engineering menus if you are keen enough. Personally I don’t like the latency you get with standard Bluetooth audio when watching tv, though. I wouldn’t bother.

On the menuing within the sound options of my Samsung 55" UHD you can set the sound to go to external speakers (my Sonos bar is connected via the optical cable) and turn the internal speakers on or off. With a sound bar it produces a weird echo, but if you took the Optical out and ran that to a TV streamer you’d be fine. You can then independently adjust the TV volume while using your TV streamer to set your own volume.

I assume that if you need to decode the Optical signal and output that on RCA plugs you could get an adapter on-line. Or buy a set of headphones with an ‘Optical-in’ for yourself for Christmas?

In his case it would be optical to a dac to his Sennheiser headphones base station but it should work. Assuming anyway that optical is always on (which it is on my tv and many others) regardless of what the audio settings may say.

What brand and model of hearing aids do you have

What does that matter when the OP wants to use their Sennheiser wireless headphones?

I too am hearing impaired with a wife that needs a lower volume that I. Here is my solution:

My system Samsung TV 4K UHD (JS8500) and new Samsung 7.1.4 Harman Kardon soundbar (HW-Q90R).

Basically, I wanted to connect my new Bose headphones (Bluetooth) into the system so my wife can adjust the sound to her comfort level and I could adjust the headphones to my level – the key is being able to do that simultaneously. Optical connection (forget HDMI ARC or regular HDMI for this solution).
This is how I solved it inexpensively for around a $100:

Optical connection from TV Optical connection to Digital Optical Audio Splitter, in port (mine was a 1x3; 1 in port, 3 out ports) in port. Make sure you get a powered unit for better signal consistency. Cost me $22.00 from Amazon. (note: I used J-Tech Digital Premium SPDIF TOSLINK Digital Optical Audio 1x3 Splitter)
Optical connection from Optical out port #1 (of splitter) to Optical in port on soundbar

Optical connection from Optical out port #2 (on splitter) to Optical in port of Blue Audio Transmitter for TV (it also has a 3.5mm connection for wired as well). Make sure you get a powered unit (mine could power BT 4.0 to 2 headphone sets and each could control volume undependably from each other). Cost me about $69.00. I used MEEaudio Connect Universal Dual Headphone and Speaker Bluetooth Audio Transmitter for TV (AF-T1)

Simply pair the unit.
We now have a system that my wife can control the volume of the soundbar system; and I can control the volume independently in my headset – both work simultaneously and great!!