I found that the NuForce uDAC2 improved the sound from my computer when listening through the speakers and through the headphones.... and I know there are better DACs out there. the uDAC2 cost is around $100, so it should not break the bank. I am not necessary recommending the uDAC, but a DAC in general.
Be advice that this will probably happen to you also... as I started enjoying my new "head-fi approved" gear, I found out that 70% percent of my music was encoded in low bit rates (128)... so naturally, I am now in the process of re-encoding / buying everything again.... HAVE FUN!
Just be aware that the sign of "head-fi approved" gear isn't necessarily worth much at all.
Take the uDAC f.ex. You'd need a pretty shoddy headphone out on your computer for it to be an actual improvement.