I found the DG amp very capable, for my HD555 the middle setting (Pro gamer mode 32-64 ohms) its enough, clean sound, no distortion..

Also check this post :) http://www.head-fi.org/t/568757/asus-xonar-dg-the-best-cheap-thrill-in-computer-hi-fi

Well the Xonar DG sounds pretty good, at least better than my Onboard Realtek and Audigy 2 ZS, it can drive easily my HD555, also its cheap (~$30 amazon), check the blind listening tests results.. in some aspects they found it better than the Xense... (http://techreport.com/articles.x/19997/6)...