I've heard of this for the X-meridian, but I was not aware that it can be done with the X-Mystique. Either way, I've switched back to my X-fi now that things are working ok. I only got rid of it in the first place because I couldn't get it working on the 680i board.
My parents have inherited my X-Mystique, and they will be using optical output into a home theater, so I don't think I'll do it now, but certainly something to keep in mind if I ever take that card back, haha.