"What u hear" function / Stereo mix (only in 2 channels?)

[sarewak]

Hello everyone.

My intention is to play sound simultaneously on two devices. Some 5.1 speakers and my wireless 7.1 USB headphones.
On my motherboard there is an integrated sound card (Realtek), which allows the "Stereo Mix" function, which makes a mix and plays simultaneously (with a small delay), in my speakers and headphones…
The problem is that my speakers that are 5.1, play perfectly since it is the native device, BUT in the headphones it only makes the virtual mix, in STEREO, that is 2 channels, so in games or 5.1 content, I lose sounds

I don't mind buying another external sound card, to achieve it. I also have a "Sound Blaster Audigy", which unfortunately does not have the "What u hear" function (what you hear), which apparently is similar to stereo mix.
I have seen that there are others, like the Sound Blaster Z, which does have said function, but of course, if it does the same thing, it's not good enough for me.

What I need is to duplicate the sound, so that it is emitted at the same time (even if it has a little delay), but that duplicates in the 5 channels, and not just in 2 channels as "Stereo mix" (as its name indicates "stereo mixer").

Thanks and regards!!