I think you also need ports 6000 and maybe 7000.
Are you able to host games on Ironclad Online that people can join? Try hosting a game on ICO and see if your friend can join that game.
Is it possible that you and your friend have different versions of Sins or that one of you has a mod installed the other guy doesn't?
Another possibility might be that one of you has the dreaded (but easy to fix) mesh error problem. You can test for that out on ICO by seeing if you can join other people's games and vice-versa.