i would doubt there would be much in either performance or sound quality...the difference between the two comes mainly between the features, supported standards, and software package (the Value has, IMO, a "healthy" sized software package...not nearly as bulky as the ZS'). but the gold-plated connectors MIGHT make a difference in sound quality...
i dunno how much difference the additional THX configuration utility would make either...
as far as i can see, they follow the same gaming standard (EAX 4.0 Advanced HD), although the EAX 4.0 Advanced HD drivers havent come out for the Audigy 2 Value yet.