Unfortunately the plugins are only availible to licensed customers.
You can't access them just by signing up to the forum.
If you are after a demo of the integrated 3dMax plugin presently there isn't one.
Although Refractive promised one quite some time ago it hasn't been made available yet and I can't give you a likely date either.
If you have specific questions about that plugin feel free to ask them and perhaps an existing customer can assist.