Asus Xonar is the sound which i bought recently 
i was using an on board 889 realtek audio chip perviously. As per the review that are given by OCC and other reviewing sites i dnt find that sort of a difference basically it depends on what genre r u listening more over from song to song that i ll cover in detail in the review . If movie being taken into consideration it outperforms various cards from creative ,auzentech. Comes with SPDIF out and thats the key to get lose-less sound production where the sound being processed at 192khz . Even with a analogue connection (3.5mm jack speaker /headphone) u r able to find out the difference pretty soon. 
Talking about Xonar Audio Center its fabulous having variety of options "For PPL HAVING A 2.1 channel SETUP DNT EVER TRY N Listen to songs in the dolby mode all the details will b lost. The best mode to listen songs is the Hi-Fi one or u can even adjust as per ur preference via the equalizer. With Xonar Audio Center u can even adjust the sound reception by adjusting the speaker placement and the size of the surrounding. Again a NOTE- ppl havin 2.1 setup wont be able to see that much difference so better USE headphones n ur eyes ll pop out once u use xonar audio center and ur headphones jacked in .
 
 
I for the sake of testing my xonar heard music continuously for hours every time i got a different result Depending on Genre and moreover the song. Once u jack in xonar the first difference u figure out is tht ur BASS HAS GONE MORE DENSE their is more richness in the bass and ur able to hear every instrument very easily (sound stage expansion) . Acoustics were like hell amazing Vocals got amazingly clear.
For xample i heard Fade to Black from metallica 
I was able to hear the sound of plectrum every single tym it hit the strings and when Lars ulrich struck the cymbals the sound was amazingly detailed crisp was lasting for a longer tym unlike when i used to hear it on my onboard it used to fade away. It sounded 60% better compared to what i heard with my onboard. 
the least difference will b xperienced in Trance and electronic genre with Xonar Dx 7.1
On the whole its at least 35-40% better then ur Onboard audio.
For Movies its hell amazing .