In Windows 10/8/7 the lesser used devices including the WaveOutMix, MonoMix, StereoMix are disabled by default. If your sound driver supports this feature, you can enable it. This post shows how to to enable all Recording Devices and make Windows show even the disabled devices.
Make Windows Show Disabled Devices
To make your Windows show all the disabled Devices, you have to right-click on the Speakers icon in your Notification Area and select Recording Devices.
Next in the Sound Properties box which opens, right-click anywhere and select the option Show Disabled Devices.
This will show the disabled devices. Select the recording device/s and click on Enable it.
Click Apply > OK.
You will have now enabled even the disabled recording devices on your Windows computer.