Even if the motherboard audio has improved a lot they will never compare with a usb soundcard/dac, my advice is to buy any motherboard you like and it is compatible with your cpu and buy a separate usb soundcard/dac. As soundcards there are a few profesional grade cards from creative and asus, as dacs i cant tell you anything about that. I myself got an asus xonar u7 and i m pretty happy with it.
EDIT: Gigabyte moterhboards has a special usb port for usb soundcards/dacs for a more stable current without any ripple noise so i would start from there.