Hi Hans -
Envolve is designed to let you have people sign into *your* forum and not into Envolve. You can turn this on very easily from our backend at
http://www.envolve.com/admin. Just click on your site after you log in, and then click on "Options". Then choose "Redirect sign-in attempts to URL" and enter the URL of your sign-in page. (then click Save).
You can absolutely have subforums through Envolve. You just need to use our "grouping" feature:
http://www.envolve.com/api/user-grouping.html
We understand we are an expensive option. We are working hard to make sure we are the *best* option though and are worth the price.
Thanks for trying us out!