You won't notice great differences in the audio cards, but you will detect great differences in the speakers. If you budget is limited, spend the money on speakers that are quality and protected so they don't get blown in the first few days that you have them.
I would buy the speakers first, then buy the speakers later (Even if you have speakers now). Buy the audio card with what is left, or buy it later, if budget is an issue, because bad speakers can blow an audio card. Good speakers can make even a bad audio setup, even integrated, sound pretty good.