3
Your current site is based on Frontpage source code. This is mainly static HTML content all of which can be duplicated on a XOOPS platform, Plus you get all the dynamic interactive features that XOOPS offers.
I would forget Front page, its a pain to update and very limited. To use XOOPS only as a backend, or add-on is to missunderstand its full potential and flexibility as a CMS.
Why not build a XOOPS site and see how much existing content you can get into xoops? Then build on the future features you want!