usb dac

Hi,I find myself more and more listening to internet radio.Presently i am using M audio fast track sound card .My question is: Would gettig a better dac like Wavelenght brick or Bel Canto dac-3 improve sound? Which of these two would you recomend?
Also,how could i connect my own dac to pc?
I thank you in advance for your input.

The best USB DAC sound I have hear was from an Empirical USB to SPDIF feeding a Theta Gen VII

That was the ONLY time that I experienced a USB sound source bettering a CD Player( It was the AR CD Player).

Your Milage May vary ;-)