Issue with setting up remote bluetooth speakers

I have a bluetooth connected in-wall amplifier (IST-I600) in the room next (Playroom) to the location of my computer. I want to be able to have music playing from the computer on both the system speakers (HDMI connected TV and speaker bar) as well as the bluetooth connected amp in the next room.

I have already run an extension line to get the bluetooth radio as close to the IST as possible (within 5 feet).

I have connected the bluetooth.

When I switch the primary playback speakers to the Playroom system, it send the music there perfectly.

I have set up the record side to use Stereo Mix to use the Playroom system as the "Listen to" destination.
The Stereo Mix audio bar "dances" with the sound, but the Playroom audio bar is blank. No sound comes out of the Playroom system.

As far as I can tell, for some reason I can't find, the sound is NOT getting from the Stereo Mix to the Playroom destination....

Please help????

Sort of.
I had found the instructions for setting up bluetooth speakers with the wired primaries and having them both produce sound. In fact, my set up worked for a short time. Then suddenly it stopped. It requires using Stereo Mix to play back through the bluetooth. My problem now is that for some reason the Stereo Mix is not getting the sound to the bluetooth output.

BTW... My HDMI connection to the TV is via a converter, not an HDMI output on the computer.

The HDMI converter connects to the VGA port, a USB port (for power) and the green speaker jack. It is set as the default system speakers.

Yes, I have that same tab in Stereo Mix Properties and it's set at full.

Yes.

The main speakers on the TV, which pulls its sound through the green speaker jack on the back and routes it through the HDMI converter work fine as System Speaker (default).
When I switch the Default to the bluetooth connection to the remote panel, IT works fine (of course the System speakers turn off as expected).
Now, the trick to getting a second set of speakers to work is using the "listen to" feature on the Stereo Mix function of the Recording portion of the sound controls. Set the Stereo Mix to be heard through your second set of speakers.

My problem is that for some reason Stereo Mix won't send it's listen to output to my bluetooth speakers. The status bar dances on the Stereo Mix, but the remote panel indicator stays blank.