There is no sound card that you could buy that would upgrade your sound. Like fmw said, you now would have to upgrade you speaker system to get better sound. BTW sound quality is not affected just by speakers but by source and amplifiers as well, Speakers can only be as good as their source. The Z5500 has an integrated amplifier system for all the speakers and although it is a good speaker set for computers it is not good for quality audio listening. If you really want an upgrade you would have to go a home theater system. You could buy a Receiver with integrated amplifier or get a Preamp and have separate amplifiers for each channel or paired channels (stereo). If you are interested I could put a list together for you. This would be the only way to upgrade you sound. Hope that helps.
