We operate forums for a number of sailboat brands. They all use the same domain but different subdomains, i.e., hunter.domain.com, oday.domain.com, catalina.domain.com.
Some of the specific forums only appear on certain subdomains, and some of the specific forums are shared by all of the subdomains. For example, a forum only about Hunter boats would be listed only on hunter.domain.com. And a forum for owners of all boats would be listed on all of our subdomains.
(I know your software isn't designed to do this out of the box and some modifications would be required, but that's _my_ problem...)
We run all of this from one VB installation.
How does this translate to a Xenforo licensing scenario?