Other aspects of the issue include driver quality and CPU usage.
It used to be that Creative had good drivers and onboard had crappy ones.. now everyone seems to have crappy ones.
Separate add-in sound cards can save CPU cycles as well, though you have to get the right ones. Important if frame rates in games are the #1 factor for you.
This is the card I think I will get for my current computer:
http://www.memoryexpress.com/Product...22953(ME).aspx