This tutorial focuses upon using the Donationware (free to use, but make a donation if you like it) piece of software called Voicemeeter, a combination “Stereo Mix on Steroids” (my description) with TWO virtual audio cables as part of the download and installation, using this in conjunction with the OBS or Open Broadcast Software video window/monitor/capture card/webcam/camera mixing and scene arranging tool.
In this video, I bring in the microphone input from a USB interface (Focusrite Scarlett 2i2), Foobar media player, Audacity audio playback, Skype (which also gets the mic feed from this) all going out to OBS and being selectively monitored through my USB interface and its headphone jack (I chose not to monitor the headphones via the software due to the slight delay, since the Scarlett 2i2 has hardware monitoring built in for the mic).
Foobar Media Player (also would work with VLC and WinAmp)
Skype receiving: WELL… in this video, all the above, but another video here shows it NOT getting its own audio… do not follow this one for bringing Skype in!
(I just wanted another audio source to show this software off with…)
Here is the Skype technique