A8N5X Motherboard has no audio when chassis/case ground cable is connected to an USB-ground connector
When I first tried Colin McRae Rally 4.0 on this motherboard, there was no audio.. not to worry. Few minutes later I find out there is no audio in Winamp... ouch. I go look at the audio panel that was installed along with the drivers. I disable SPDIF.. nothing helps.
I go back to the store, hoping to get a quick replacement and the store-owner quickly look at my internal connection on the motherboard and says.. oh wrong connection here. You plugged the case extra USB ground connector into an empty USB slot ground connector, and for a reason I don't know it cause weird kind of problems. Fortunately audio comes back alive after deconnecting the faulty connection.
So if you get no audio on your Asus motherboard (or A8N5X model), unplug all case connectors first, or at least leave unplugged the extra USB ground from the case.
Why on the user manual, when you look at the USB connector pinout, the pins are labeled USB+5V, USB_P8-, USB_P8+ and GND since when this GND is connected to the motherboard ground it causes components to malfunction. This GND should be labeled USB_P8-GND since it is not the same as the motherboard/power supply common ground.