I have been perplexed by this combination not yeilding the performance gains seen when using the Audigy 2 with an Intel CPU.
After doing a bit of research (I cannot stand not knowing why things act the way they do), I have narrowed it down to what I think is possbily why.
The Creative drivers are making use of the SSE2 instruction set (when available) for streaming the audio. On Intel CPU's this appears to be more efficient than on AMD, which could explain why Intel users typically get a better boost in performance than AMD users do.
Next step is to find a way to disable the SSE2 instruction set usage (they do detect it and use it if it is available) and see if it could help AMD users out.
More later....