Well, at last some actual information about Skype's "failures".
I am expressing an opinion when I say that Skype fails completely to deliver audio when the host computer OS (Windows) is set to output 5.1 sound and that an app like Skype that absolutely depends on the best audio possible under the circumstances need not fail in such circumstances.
Your reply explains why the Dr. killed the patient but does nothing to justify the act. We do agree that Skype audio fails in 5.1 mode.
Skype, on loading, could check the environmental sound settings and issue an error message if it discovers an environment known to cause audio failures. This would be the least demanding task for a motivated programmer.
Or, Skype could engage an audio transform "app" that bridged the well-known gap between telephony analog "bit rates" and the demands of 5.1 surround sound. Some sounds get through accurately so the transformation may not be complicated.
How about a script that switches Windows to and from Stereo <-> 5.1 Surround that runs when Skype is loaded and gracefully terminated? Just a couple of mouse clicks for me to do that.