Hi Scott
Open Skype
Go into Tools, Options, Audio Settings and choose the line in option
Uncheck the box that says “Let Skype adjust my Audio Settings” and then click Save
You will then need to experiment with microphone settings on your external mixer.
If you do not uncheck this box then every time you alter a setting on the mixer, Skype will alter its own settings. (This can cause some pretty weird things to happen) Use the Skype test call to adjust your microphone.
Hope this helps

Bill