Once you have the local viewing setup for your Slingbox your done with its configuration. The only thing that's preventing you from remote viewing is your router. And opening up your network to the world is a very bad idea, and not to mention isn't going to provide access to your Slingbox.
Slingbox provides its support through port 5001 (by default) and that's how you access it from your private network and public network. However, your router has certain services to provide you with a safe networking enviroment. Unfortunately, these services are also preventing you from accessing your Slingbox remotely. One way to allow your Slingbox outside of your network is port forwarding. Without port forwarding any internet request for port 5001 will be ignored. This is because your router doesn't know which of your networked clients will handle it.
When you configure port forwarding on your router, you specify port 5001. This is the port which the Slingbox provides its services. So, the next important part of completing the port forwarding rule is the IP address of the Slingbox. Once you've completed setting up the port forwarding rule, all of the outside requests for port 5001 to be directed to your Slingbox.
Here is a website that helps people setting up port fowarding, http://portforward.com. I looked up your specific model and found the following page,
Another alternative is Universal Plug and Play (uPnP) its a set of protocols that allows to devices to communicate with one another for configuration purposes. I noticed your router is uPnP compatible but its services is disabled by default. That explains why the Slingbox Assistant couldn't complete when it started running for tests for internet viewing. If you can find out how to enable uPnP on your router then you can rerun the Setup Assistant to allow the automated configuration to complete.