Why does my audio still suck even though i upgraded my audio card?!?

When playing crysis with onboard audio it would be horribly stuttery, and on youtube, videos had popping sounds and sound would fade in and out. I eventually upgraded to a Diamond xtreme sound 7.1 card, but there is no improvement. I uninstalled the onboard audio but that didnt help, so i uninstalled the drivers for the onboard audio but Vista promptly reinstalled them.