Apart from the MS UAA driver, which is a good idea actually, try looking in the BIOS and see if the onboard audio is enabled.
If it is, try disabling it, as it might conflict with a PCI audio card that is inserted in the motherboard.
If you see a device in the "Unknown" or "Other" devices category (or even in the Sound, video and game controllers category), check the hardware ID, as that will tell us what exact audio hardware is present in your PC.
You mention you tried drivernavigator, but that's actually not one of the better programs. Try driverfinder or driverdetective. I have used the first and their support is better than most I have tried.