Personally i think you should stop worrying about your speakers, i don't see the point in buying better speakers if your current speakers are not being put to full use.. (which i highly doubt they are).
I would think about getting:
Faster Memory - Possible Overclocking (perhaps some OCZ PC4400 Voltage Extreme)
Another 74GB 10,000RPM 8MB Hard Drive (Put them in raid)
A new case: Antec P160 - really really lovely case, can't fault it
Or perhaps a new processor? 3700? 3400?
Or even better, get some Dolby Digital Headphones (3D Surround Sound), they are amazing.