Hi Fusby,
I also have never used the XFI and i don't ever plan on doing so. I personally thing this "gaming" and "music" branded sound cards are a waste of effort...the audigy 4 is better IMHO.
However...EAX should be set in the game...and no other settings needs to be altered.
Mic Enviroment Fx will just add sound effects to your Mic input...so you can make it sound like you're in a big emtpy hall...or at a live concert...or whatever the options are
Hope this helps.