Eventually you get what you pay for . You cannot say Xonar DG is crap by comparing it to a 8k sound card . For the sub 2k budget the Xonar DG is the best card out there and i can tell you with confidence you will get better O/P with it than with a onboard sound card . For the sub 5k budget there is Xonar DX similarly sub 8k there is Xonar Essence ST/STX (prices have increased now ) .
So based on your budget you can go for one these 3 , however if you are going for a 18k speaker i would recommend you to buy a Xonar Essence ST/STX since it will complement your audio setup well than a DX or a DG.