This may be a super obvious question, but I'm using my Eleven Rack as my PC's audio interface/sound card and purchasing headphones with a mic for gaming. Obviously, I can plug the phones right into the front, but how exactly do I connect the mic? Thanks!

Surely someone has some insight?

Use the line input at the back, use the switch at the back to select the right line level (most likely -10db since that is a consumer level device).

Thank you, kind sir!

No problem, we are here to help!

Unfortunately, I'm not able to get the mic to respond when following your advice. Have it plugged in to one of the line inputs, but can't get a signal from the mic. Tried playing with all of the different options in Windows recording devices and you can see the level of the output, but the thing's just not producing. Any advice?

I am going to have to assume that you may not have configured the input. From the manual:

To choose which input is routed through the Rig:
1 Hold the Edit/Back button for one second to bring up the User Options screen.
2 Use the scroll wheel to select the Rig Input User Option.
3 Press the SW1 button to enter the Rig Input menu.
4 Set the input you wish to route through the Rig with the illuminated control knob.
5 Press Edit/Back twice to return to your original view.

To ensure you hear your audio when using Eleven Rack as a standalone signal processor, be sure to set the Rig Input User Option to the type of input you plan to use (Guitar,
Mic, Line).

If that does not work check the line level switch, it may need to be in the +4db mode

If you do not have it, highly recommend downloading the manual (http://akmedia.digidesign.com/support/docs/Eleven_Rack_User_Guide_v90x_71670.pdf) lots of good stuff in there

BTW are you using pro-tools or another DAW?

Another thought, you probably need a mic pre-amp to go into the line level input.

If my other advice does not work. Another option is to buy a XLR to female TRS converter (or make your own ) and use the mic input on the 11 rack (http://www.amazon.com/TRS-Female-XLR-Male-Adapter/dp/B0024X7XL0).

This is probably the best option as it will allow better control over the signal (pad/gain).

Here is the explanation why: http://www.ovnilab.com/articles/linelevel.shtml