For your second question, you won't be able to listen to the 'same' thing thru your onboard output and your sound card output. You can route differnt apps to play out of each, but the the same app;
IE: You start a game, with your Sound and Audio Devices (in the control panel) set to the sound card for output. Then after the game starts, you switch it to your onboard sound card, then open Windows Media player and play some mp3's, they will play out of your onboard outputs. But, I'm almost positive you can't do this with a single source.(meaing you can't have the game sounds play out of both).
You can also go into the Windows media app and change the output source, and this may be a possible option for some games and other applications, but not all.