Your motherboard uses the realtek 898, their top of the line codec. But I recently chose to go with a x-fi titanium over a realtek 898, because of all the customizations you can do like the crystalizer and stereo expansion. However, I've got it hooked up to a 7.1 surround system.
I'd use the onboard for music or movies, and go with the x-fi if you are a gamer.