Thanks for the info.  I ordered the exact card you named strangely enough - Xonar DGX.  Was going to go the high end route, but from the other reading I've done return on investment seemed minimal.

Hello,   I just purchased the Sennheiser HD 598 to hook up to my PC.  I'm simply using onboard sound right now and have the headphones hooked directly to the headphone slot on the PC.  I'm hearing a steady hissing in the background of music, most likely due to my poor setup I'm guessing...