Its been my experience that specific forums are actually some of the hardest to populate and monetize.

The primary problem being, until you have enough 'posts' on the forum, you are going to lose traffic because surfers will see the board but, think it isnt busy therefore not post.

That being said, a work around could be to create a broader forum and use the domains you have as feeder forums but, this is going to mean that you will need to have a main forum that is reasonably busy before you can utilize the domains to create sub forums.

IMHO you are going to see much better results by creating a forum with a wider appeal then branching that out in to several smaller forums than creating several smaller forums from the off-set

Hope this helps.

Regards,

Lee