The Audigy 4 OEM is the Audigy 2 ZS rebadged. The DACs are slightly better than the vanilla Audigy 2, and bitperfect (also known as no sampling) is available through the digital out (not exactly new for none-Creative cards, but a Creative first).
If you are talking about the $250 Audigy 4 Pro, then yes, it is quite a step up electronics-wise from the Audigy 2.