hellothere
“900Mz unit” is a wireless Analog Headphone as opposed to Digital BlueTooth. They usually work at a 900Mhz FM frequency. The Sennheiser is a popular model : http://www.4homespeakers.com/wireless-tv-headphones.html
What I don’t like about them, the receiver is in the headphone and therefore it’s rather bulky. I use to use a system like it but the receiver was a belt-pack and I could use earbuds for more comfort.
That was before I had HA.
You had mentioned a Soundbar with BT, that made me think you could use the TosBlue Telm2, it does pair with two devices and drive the BT Soundbar as well as the BT Neckloop at the same time. That would definitely sync the sounds up to the Neckloop. I don’t know if there is a lag from the Neckloop to the HA.
Could also use less expensive Bluetooth speakers.
The TV speakers would be turned off.
My Soundbar doesn’t have BT, I would have liked to try this.
And if your TV has Audio Delay adjustment you now could sync the picture to the sound.