The PCI-e version is like an Audigy 1 in that it has no hardware signal processing.
This limits it to using a max of EAX 2.0 and it requires the CPU to process the sound.
It cannot do EAX 3.0, 4.0, Advanced HD 5.0 etc.
Dont get any X-Fi that is an Extreme Audio, they are non hardware accelerated cards.