How to output audio to multiple devices in Windows 11?

I have tried multiple ways including the suggestions here.

Unfortunately there has to be a way for Microsoft to allow the following

The bottom WIFI Speaker is hooked up with a proper stereo wire (left & right channel) but there is only one selection allowed.

Unless I am missing a step to allow both to light up as pictured below.

Or is that possible?

So, is there is no way to pass the same audio output to two different output devices with Windows 10/11 sound.

Output #1: A line out on installed card to a stereo speaker system.

Output #2: Bluetooth audio headphones to monitor the #1output feed.

Example: I cut the line-out house stereo for a moment, I would like to continue monitor the feed with headphones and vice versa.

This was a configuration that I had used at one time with a Win 7 box and 2 SB sound cards.

Absolutely agree. This feature is necessary and works as dual Audio on my phone out of the box. If both kids in the plane or car wants to share the audio of a game or stuff like that on headphones its nessary ... and 3,5 headphones and y cable is kind of 70s.

This doesn't work at all for me, in fact when i follow these steps both devices stop playing audio and i have to disable stereo mix to get any audio back, i tried playing with the settings in stereo mix and nothing worked to even get one of my devices to play audio while stereo mix wasn't disabled

can you tell me how you mobile does this sound mirroring thing.