Wow, you have a ridiculously over complicated setup. I can't begin to understand how its connected by your description. So, here's an article (http://support.slingbox.com/get/KB-005033.html) that may help you.
As far, as troubleshooting goes, its probably best you connect the Slingbox and a computer to the same router via ethernet cable to see if it works locally. Then you can start branching out into the complication of your network.