Considering the subject and content of your site, I think the majority of your traffic would come from search engines. Although you said the site has been heavily SEOed, you'll want to make sure you put a large amount of your effort in trying to gain good positions for the keywords in your articles.

You can also try marketing your forum before the main site itself. For example, you could try holding a large posting/referral contest on your forum and then advertising the contest on some large gaming forums (if you could offer a Xbox 360 as a prize, you'd get great results considerring the Xbox shortage ). As the new users visit your forum, they will gradually stumble upon the rest of your site.

As Animus said, you can also try gaining traffic by talking directly with your visitors. If someone on Xbox Live says "I can't figure out how to hook up [instert Xbox accessory here]. What should I do?", you could say "Check out GetXbox.net - they have an article just for that!".