Creative X-fi Gamer/Music is where I'd go next to be honest.
I uprgaded my Audigy SE to an X-fi Music, and I was blown away by the improvement, even though the Audigy was better than onboard.
The X-fi Gamer/Music also process in-game sound helping reduce the CPU overhead.
The X-fi Extreme Audio is probably worth avoiding though, as it's a cut-down X-fi without the features of the two I'd recommend.