What are you going to be doing with the PC as far as sound goes? Also what speakers are you using? The quality of sound you get is more dependent on your speaker setup imo. If your planning on using mainly headphones, the onboard will be fine.
ultimately, since the board you are looking at does have onboard audio, i would try that out and see how you like it. If its not acceptable for you, then consider buying a soundcard.
I am using the Ambx gaming peripherals speakers and I use headphones occasionally, but your idea is great. Thank you