as I'm under the constant belief that the sound card would not only remove the load from the cpu (now gpu), but will give that extra kick!
The load removed from the CPU is minimal. Don't even consider a soundcard as a way to increase FPS in game.
So, my simple question: will the addition of a sound card do the trick without my having to upgrade my headphones? I'm not looking at upgrading the headphones as of now.
Depends on the headphones your using. If your using a $10 set of headphones, you probably won't notice much of a difference.