X-Fi's are the WORST cards on the market, not the best. Both ASUS (C-Media chipset) and HT Omega (also uses the C-Media chipset) have better cards then Creative. Heck, even though Auzentech uses a X-fi chipset, they at least put decent Oamps on the cards to give significantly better quality.
HT Omega only supports EAX 1-2
ASUS supports EAX 1-2, and support for EAX5 via emulation [works very well in the games I've tried]
Auzentech supports the full X-fi spec
And I should point out that X-fi is more or less a dead standard now; very, very few new games use X-fi at this point...