Yes, you can buy front panels with all sorts of inputs - like I said, the headers are standard. I bought a media front panel for my htpc and it just plugged into all the spare headers I wasn't using. Of course, a rear connection is better if it's a permanent connection so you don't have to live with a PC with a cable sticking out the front and snaking to the back.
Depends on the sound card, but it should show up as a separate audio output device with digital in the name to separate it from the analog output. Just make it default and all audio will be sent through it.