Windows 8 64bit, and drivers for win7 64bit installed flawlessly. However there are unofficial "unified xonar drivers" and they don't work with win8, but this will probably be fixed soon.
My choice for Xonar DG was after I've read many reviews on the internet (more than 10 to be honest). All of the reviews more or less agree about the noticeable difference (both subjective and objective) of good onboard sound vs Xonar DG. There were only 1-3 reviews who said the difference couldn't be felt or was too little to matter. Well, now that I have this card, I disagree with them.