lowyhong: I read somewhere that games today use more resources for sound. You have things like ambient sounds, reverbs and echoes etc, which take a lot of processing power away from the mainboard. Not sure if that's true, that's why I'm asking.
It is, but depends on the game, and how it processes music. If the game uses OGG / MP3 / some similar crap, you can forget about the CPU using more power to process the audio. It would be barely noticeable, like only a few FPSes out of the hundred that you'd normally get (if the game didn't have any audio). Sadly, most games tend to use this crappy way of presenting us the atmosphere / sound / whatever that you can hear.
If it uses raw audio, has complex algorithms that process the sound in real time (and not just to select a track to play, like most games out there), then the sound card upgrade wouldn't be a bad idea... if you have the hardware to make use of it.
Using headphones / speakers?