DX9 is the prob, i had the exact same prob with a sblive and win2kpro.
I downloaded dx9 Web ver, had that prob and another, ONLY 1 speaker would work and, at that the rear right one. So i used DirectX 9 Uninstaller, it works on XP and 2k only.
You can get it at
http://www.guru3d.com
Anyway after uninstalling it i went back to dx 8.1 everything worked like it should again. Few days later i decided what the hell lets install the redistrubation version of direct x9 this is supposed to be the same as the so called download off web ver, but it contains dx for all versions of windows, and can be installed off a hd, cdrom, or whatever you want. It is almost 32mb and you can get it here
http://www.microsoft.com/downloads/details...&displaylang=en
installed, and havn't had a prob. I dunno but i think the WEB version, is missing a few critical files, So download the redist and try it.