Re: Several domains
Why not redirect them with a permanent 301 redirect? If your host does not offer this, why not create a directory for each domain, like this:
You install bbPress in the domaina.com/ directory. In the domainb.com/ directory, you put an index.php file in there like this:
header("Status: 301 Moved Permanently", false, 301);
Then, when anyone accesses http://www.domainB.com/ they are seamlessly directed to http://www.domainA.com/. Would that accomplish what you need?
You can also use .htaccess for 301 redirects if there is more than one page, like there are search engine results with pages from domainB.com already out there, and you want to redirect them all to domainA.com.