I hope you haven't given up yet. I'll try to help you out.
Just a warning that this is going to be a little complicated because of your current set up with 2 devices acting like routers but we should be able to get it figured out.
Two Questions
1. Is your Mac Mini connected wirelessly through your airport or is it plugged in? I'm not familiar with the port setup on these.
2. Can your Mac Mini be plugged directly into your WiMax router? It would be nice to eliminate one of your routers from the equation if it were possible with your current setup.
Let me know these answers and we can get started.
