The first answer was perfect. Here is my response to an earlier question and it might help you make a decision:
Have you tried downloading the driver for the HDAV which is basically a Xonar Essence PCIe card with a different hood on the engine? It is 50 MB compared to the 11 MB for the STX driver. The bottom line is; Asus should be ashamed that they continue to sell this sound card for $187 and have not improved any of the software/drivers since 2010.
Seriously, I have worked "inside" the walls where large corporations have to communicate with one another and plans are basically finished 2 to 4 years ahead of a major product release. If not, who could build anything that wasn't thrown together at the last minute?
Long ago it became known that sound cards would be unable to compete with CPU sound, chipset sound, MB sound, USB sound.... and companies like Creative which were slowly dying in the increasing temp of the water in the beaker, finally got wise (or hot enough!) and jumped out before they died.
Asus jumped out long ago but tried to look like they were "all in". They purchased a "Google Bone", and simultaneously tossed out a poorly made sound card that was nothing more than a Xonar STX, named "Feebie" instead of "Essence". When they hit their profit goal Asus quickly abandoned ship.
The problem is; the boat is still floating around, and whenever an "MB-sound-only user" sees the "Loch-Ness" the excitement level bounces back just enough to keep people buying!
To say it is all speakers doesn't quite do justice to all that is involved in taking a "physical" phenomenon and turning it into an electrical signal in a variety of forms, and then bring it full circle so that it physically pushes the eardrum; otherwise Marantz and others have been duping people for 50 years with these giant heavy receivers!!
I hate to see it happen but the "smaller is better" foolishness is going to suck the sound card along with the video card into the CPU of Moore's Law.
You have to laugh, especially when you are reading an article describing the Surface? All the hype with its amazing graphics and such a small weight; while you are holding a 6 pound EVGA780 6GB in your hand getting ready to install it!
Somebody is not telling the whole story and that is why the Intel Map has always had to versions; one for the public and one for the treasure hunters!