Have you tried going into device Mng. and disabling the onboard sound from there??
Unfortunately I am running LInux, so just having it on the PCI bus is causing issues. Since all (most) of the HD sound drivers use the intel module, I rely on the BIOS to do it's job and remove it like it is supposed to.
I can blacklist the PCI id, but I was hoping this was a known issue and they're working on it or something, but I guess not. Plus, this system has a lot of I/O serving video to the entire house, so keeping the interrupts to a minimum greatly increases performance.