now as you have tried expensive headphones then you need a great dac and also a great amp(both are as important as the headphone)... you need good power to drive high impedence/costly headphones... although audiophile equipment goes in lacs but i will only tell you the stuff that is affordable and does the job with a bang... i recently bought the following gear from abroad through people
asus xonar essence st(the dac is incredible and the amp it has can drive most headphones but i would still recommend a seperate amp)
fiio e9 desktop headphone amplifier(this thing is affordable and powerful...i can power any headphone out there)
sony mdr-xb 1000(worlds most powerful and biggest headphones with the heaviest bass)
sennheiser hd650( one of the best out there)
sennheiser hd598(great sound and incredible for gaming)
this cost me around 1.5 lac total... it is neither high end nor low end... best bang for buck stuff... medium end sort of....
your original question is about soundcard so get the asus xonar essence st... it is the best out there without a doubt...