How do I properly label/wire a switched subwoofer outlet?
You'll need to pick up a PowerBridge type device, they allow you to have an inlet in one location and an outlet in another.  



You'll connect the inlet to the outlet using cable rated for the appropriate load (14/2 Romex most likely), this insures everything is up to code (since it's not proper to run extension cords through walls). 

To make the outlet switched, you'll simply connect a switch on the hot wire of the cable between the inlet and outlet devices.