Forum plugin recommendation?

I would like to run a forum on a sub-site on a multisite install. Subdomains, but domain mapped. I've tried Simple:stuck_out_tongue:ress and bbPress, but both redirect to the main site for registration and login, which I want to avoid.

Anyone know of a forum solution that can run on a domain mapped subdomain installed sub-site on a multipress install that doesn't redirect to the main site for registration/login?