I'm an audiophile and when I lived with my parents I had a very beast audio setup. Back then it was basically "required" to have a sound card for 2 reasons.
1) Single core "weak" CPU that needed as much offload as possible
2) Hardware audio acceleration with EAX.
These days since I traded off my PA for more visual because I live in an apartment I have everything going through some JBL Creature 2.1 speakers. They are tiny, but the audio is actually quite nice compared to some stereo speakers I have heard. Since I can't really turn it up I have felt no need to upgrade my system and I have had this problem for probably the past 4 or 5 years. Hence, no speaker upgrades since I got these. That being said, I feel there is absolutely no need for a sound card because these speakers warrant no need for the extra quality. You really need a very good quality setup to warrant the need of a sound card to tell the difference between that and onboard.
My headset is a Turtle Beach X12 set. I only use these when I play BF3 with my friend or when I go to a LAN.