It's unlikely the mic uses that channel. How was the mic going to get back to where it needs to be?
As to three audio sources, I'm thinking some audio mixer or switch. Amazon or google for that.
So, in my basement I have a Samsung DLP with component and hdmi ports and jacks. It has no 3.5mm jack. Plus, I have my xbox and laptop in that room. Is there a way that I can hook wireless headphones up to all three of these devices????