Try this
I know with my Sidewinder mouse that the dpi on the fly was greyed out in W7 at first. What I ended up having to do was get an old mouse, uninstall the drivers, restart with new mouse attached and sidewinder mouse not attached, Reinstall Intellipoint, then restart with no mouse, and then plug up the Sidewinder. It fix my issues. I think this might work for you since everything else is working correctly and the Volume knob on our KBs is a non-standard volume control. So I would try that little switcharoo and see how it goes. Let me know!