multisite on IIS7.5 expert needed

We've got 4 sites up and running with 99% of the kinks worked out but there are still a few things that are driving us insane.

When we enable non-www to www redirection via web.config, things start to go wrong, however we need it for SEO reasons. The issue right now is that we can no longer login to the 3 "sub sites" but can still login to the primary site. When logging into to a sub site (they all have their own domain) you get redirected back to the login screen.

We've had so many hands touching the setup over the last 4 weeks I'm not sure our settings are correct anymore..

I'd be happy to pay an expert to take a look at our sites and show us how to fix it. Looking for a fix ASAP