Its nice to see Asus giving all us audiophiles all of this love as of late. However, I'd recommend Fiio, HeadRoom, and others before Asus for this type of gear. This is, of course, great for the average audio joe.
I wonder how this compares to their STX/ST series in terms of sound quality.
it probably wont come too close. there is only so much you can jam into a usb stick sized dac
You do realize that a DAC is just a small chip the size of your thumbnail right? I don't know where you get the idea that you need something really big to output a high quality signal. For example, the Philips TDA1543, one of the best DACs there is, is smaller than most coins, but produces virtually unbeatable sound. If you have an audiio receiver, try disassembling it and examine the DAC. It's much smaller than most people would believe, yet it is responsible for producing the analog signal that is sent to your speakers. Certainly its importance cannot be understated, but its size on the other hand, is a different matter.