External Sound Card for Mac?

I'm not satisfy with iMac's built-in sound card. I always play CD in my Mac(I don't have a Hi-Fi) and with a JVC-victor headphone which has a pretty good quality. Then I find my iMac can't make use of the max quality of my headphone which I can have using my friend's hi-fi. I import .aiff files in my iTunes.

I wonder if brothers can suggest me an External Sound Card which supports Mac. Or another solution helps. Will buying a hi-fi cheaper than a external sound card(I've heard of some using FW). My budget is around 1-4xxx