are you sure they make what you're asking about? i know they make pci or pci express cards that you can install in desktops and gain firewired connectivity from, but i don't know if they make a firewire interface/adapter that gives pci/pci express connectivity-- if so, i'd love to know about it.
i love my mac mini. i beefed up the ram to 3gb, swapped out the hd for a larger capacity (160gb) and faster (7200rpm) one and went native with plugs via urs classic console strip pro-- a great sounding and very versatile plugin package.