Whiteman, the first question is "What do you use now for sound output?" If you are using a standard relatively low cost headphones, or standard computer speakers with a left and a right (maybe even 2.1, with a subwoofer) a new card is not likely to sound much different than what you have now.
On the other hand, switching from something like standard stereo headphones to the Turtle Beach HPA2 5.1 headphones is going be like night and day, and same goes for a 5.1 speaker system, assuming you have the room and take the time to set up the satellite speakers in the right places.
The main reason for changing your sound card (from an AH perspective) would be the fact that inexpensive onboard sound controllers don't have signal processors, and force the CPU to do the dirty work. If you have plenty of CPU horsepower, you might not experience a problem, but then again ....
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