not sure on the Xplosion line, but i personally have the HDA X-Mystique 7.1 card. I am loving it. But if your really stuck with something like EAX 3 or 4 then i would get the Creative equivalent like an K-FI card. but if you can live with EAX 2 then i would go for it. as i presonally like it alot better than my vreative cards. I have played all of my games on it and never had a problem with spatial audio. Mind you i do have it hooked up toa home theatre, but it should act the same on regular computer speaker systems.
My personaly Audio Setup
HDA X-Mystique 7.1
SONY STR-DE597 7.1 Reciver
Yamaha 6.1 Home Theatre Speakers
3 Reasons why i love the X-Mystique over an equivalent Audigy Card
1. DDE support (Dolby Digital Encoding)
2. Fiber Optic Connection (It even comes with a small cable)
3. The preamp circuits are replaceable
Well those are my thoughts, hopes this helps narrow down your choice.