I'm of the understanding that the Realtek chip(which I have) indicates CPU usage flutuates between 1% to 3%. Anyways, onboard is plenty good for me as even though I have 4.1 I usually use earphones. A musician friend of mine likes the Creative though, because it offers a lot for his specific needs. For me, the extra 100 bucks or so a sound card cost would be better put towards a higher level CPU or graphics card.
Of the two choices we have in Canada, Future Shop or BB, BB wins everytime. Far better staffing and some can be surprisingly knowledgable. They are more flexible price wise, at least in my experience, so beating them down can be fun and save you quite a few bucks, something a lot of people don't realize or don't even bother doing!