for the card, i would go with the htomega eclaro, it has a headphone amp, good drivers, and allround top shelf componants
http://www.newegg.com/Product/Produc...Tpk=ht%20omega . the auzen forte is a nice card, its got the standard xfi chipset and a good headphone amp but it uses the xfi chip so that kinda sucks since it uses creative drivers and with EAX and HAL gone from windows vista/7 you dont get the good stuff and just bad drivers so it is not as good as the HT but its a little cheaper. then the other option is to use onboard and go out digital to a receiver or headphone DAC/amp.
what MB are you using, onboard may be sufficient to power and have a real card on it so if you went with 80 ohm or less headphones you would be fine.