It looks like you want more than key security. I would like to talk to you on the IRC forum tomorrow night so we can diagnose the issue once and for all. I have the same router, so that can help. But also we will need to know if you are using a tool for your firewall or just using an iptables script.
In addition I would recommend flashing your router with dd-wrt so the default linksys trash can be removed and you can have reliable filtering.