The audio adapter in question is called the Xmod and it makes some pretty heady claims that have me a bit skeptical, but I will reserve judgment until we actually get our hands on one. The Xmod is true plug and play and it is Mac compatible out of the box, provided you have an available USB port (and I am assuming it has to be a powered port, so keyboard hubs are out) and are running Mac OS X 10.4 or later. It claims to enhance the audio quality of your MP3s to "beyond studio quality," making audio sound more vibrant and replacing what's naturally lost during the MP3 compression process. It also claims to give you surround sound on any stero speaker or headphones connected to your Mac. It accomplishes all this using an audio standard that they call X-fi Xtreme Fidelity, which you can read more about here.
I am 100% in favor of having the best audio quality possible, whenever possible, although I honestly don't play a lot of music directly from my Mac. Still, I can't help but be skeptical about how well an $80 USB device can accomplish these lofty goals. The good news is that we here at TUAW HQ will have our hands on one soon so we can see for ourselves just how well the Xmod lives up to the Xmarketing. We'll keep you posted!