Wait, why? The SBX-equipped Creative soundcards are better than the THX equipped ones. SBX is basically the evolution of THX Tru Studio.
I only mention THX TS because it's basically the only real alternative to Dolby Headphone for CONSOLE use. PC gamers have it easy in terms of choices. So much variety.
The Zx is just a pricier version of the Z, so it uses SBX.