Just got my new MacBook Pro and wanted to use my existing Logitech headset for making some skype phone calls. However, I cannot seem to get any input from the headset's microphone. The internal microphone works, though. The headset has got 2 3.5mm plugs. I suspect that there has to be a setting for enabling a "microphone boost" or something similar, but could not find anything related to that so far. Does anyone have an idea on that?

Thank you very much!