2
I think you answered your own question in your question. Do you curl your hair before you get in the shower? (Oops, never mind, you could be a male).
Xoops IS a Content Management System, so therefore you will need to "port" your existing site into XOOPS to take advantage of what XOOPS has to offer.
You can take your existing site and make a theme for your XOOPS site.
Dana