I have a Asus Maximus VI Formula and a Creative ZxR and I want to be able to use both audio at the same time so I will have more jacks to plug into. I tried leaving the onboard audio enabled and no sound came from the motherboard, only my sound card.
This is how I want my setup to be:
Sound card: Music headphones and speakers.
Mobo: Gaming headset and once in awhile some ear buds.
Windows 7 does not support output to multiple devices on it's own. However, it does give the ability to programs to select which device to stream audio to. For example, you can have Windows outputting sound through your motherboard, but have a program like VLC output through your sound card directly. Be aware that not every program supports this feature, though, so you may be stuck with just selecting a new default sound device every time you want it to go somewhere different.