Better sound card needed? Maybe?

So, at the moment, I have a Logitech THX stereo speaker setup and a pair of Turtle Beach DPX21's as my primary listening devices from my comp, and im running them off the on board sound card on my EVGA P67 mobo (7.1 realtek that the speakers go on) and a 5.1 sound blaster X-FI USB sound card (for the optical out port for my DPX21's).

Both sound pretty ok, but at the same time, I've been getting told quite a bit by some people on my team in SC2 that sound cards are REALLY important to your music quality, and that my devices aren't being used to their full potential.

So what I wanna know first off would be is this true? Should I be seeking a better sound card for my hardware to run off of? and if so, which one?

If it comes down to it I have about $150 I can dump on a sound card, only issue tho is I have no idea which ones are and aren't worth it since I can't exactly sit here and try them before buying them (same issue I had with headset buying, and finding the perfect ones for under $300 took a LONG time because of it.. <3 DPX21's :> ).

So yeah.. Any suggestions or opinions on the matter?

I think that without higher end speakers you won't see much of a difference. If the headphones take optical in, switching your sound card won't make a difference because the headphones essentially are the sound card - they're doing the digital to analog conversion that the sound card is responsible for.

One experiment you could try is plugging the speakers into the X-FI card. The X-FI should be a better source than the onboard Realtek. If you can't tell much of a difference between those two, then dropping more money on a higher end card probably won't be worth it.