HDR: Why so many exposures?
I agree with Greg23's comments about encoding ranges. It's also worth noting that there is a general noise-reduction effect from merging multiple shots independent of range encoding issues. For example, PhotoAcute will take multiple identically-exposed shots and give you a noise-reduced merge.
That's a really NICE shot!
Re your comment about color spaces, as long as the original shot contained colors outside of sRGB, you'd expect that kind of difference wouldn't you?
Have you tried sending the RAW's straight into Photomatix? Doing so has the advantage of going from linear to linear - avoiding conversion into and then out of gamma correction.
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