Also remember the Audigy 2 ZS accelerates DirectX sound instructions which the onboard sound will not. Is this a dramatic difference in playability? No, but just something to weigh into the equation. EAX is also something you may find nice for environmental immersion (an Audigy feature).
And yes many, many folks have gotten various items from Balthazar and been very pleased.
5.1 Support: Wow does, can't definitively say for many games I can't recall the settings but if it says "5.1 sound" or "multichannel surround" it likely does. For more info on EAX and games that specifically support the features on the Audigy 2, Creative has that detail buried in their Support FAQ section on the Audigy series. It actually lists the level of EAX that each game supports and you'll find nearly all of them support the 4.0 or less level covered by the Audigy 2. Xifi will come in time, but that's a desktop only thing for now.