most new motherboards have pretty dang good onboard sound (at least in my opinion)
im not familiar with that board, do you know if it uses the ac97 codec? or if it has someother onboard chip like creative labs or cmedia?
if it uses the ac97 codec then you may want to use your soundcard, but if it has something like cmedia then i would definately use the onboard
**edit** actually even ac97 codec isnt bad

just not as good as the others (in my opinion)