Question about Sound Cards

I am using a P4C800 deluxe board with on board sound which I believe is a
5.1.

I do some gaming, and want to improve my sound, I am looking at digital
headphones like Zalman or Plantronics.

Would the onboard 5.1 and the digital headphones give me that surround sound
that I am seeking?

Or should I install a PCI soundcard, with hardware acceleration?

If I go the PCI sound card, besides the Audigy, are there other brands that
use hardware acceleration?

Thanks for you opinions...