I've got a DX58SO, and I've updated drives based on the Intel download page:
The latest Intel Rapid Storage Technology utility displayed in this selection is version 18.104.22.1684, dated 3/19/2010. So that's what I'm running (under Windows 7, 64-bit).
However, perusing the Intel download center, I find a page for a newer IRST 10.1.0.1008, dated 12/15/2010:
Why doesn't this show up in the DX58SO list? It shows up in the more generic X58 page: