My best guess would be to go into the preferred devices under audio settings, I myself don't use Vista hardly ever so there's not much that i can help you with. Under preferred devices though you should be able to select which cards to use for whichever things you want.
Having to switch between them sucks imo.
basicly its like this I have my bose usb audio sound then the motherboard sound card and then I've got a usb headset. I was thinking if I could hook up extra speakers to the motherboard for more sound