It appears this issue exists in Windows 7, 8, and 10. Did you try that video found with that search? It's pretty bad video and some might think if you have stereo mix you don't have to find your laptop's driver for W10 but it's necessary. Just seeing Stereo Mix is not enough.
So a few of my friends and I run a discord server (which is basically like teamspeak or skype) and ever since I've switched to windows 10 i could never get Stereo Mix to play any audio. (The reason I want stereo mix is that we just want to be able to play music and stuff from YouTube.) In windows 8 I remember being easily able to just play stuff with stereo mix, but not anymore. I also use Realtek HD Audio Manager and a USB Razer Kraken headset (does not go into an audio jack.)
By the way, Here is an Imgur album with pictures of what I think you may need.
If you need any other information please ask, I just wanna get this to work.

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