EMM Labs DAC2 USB port was designed almost 5 years ago when computer audio was at its infancy. Its USB port was almost an after though, and only capable of running 44.1kHz or 48kHz only and very likely used a synchronous USB connection (par for the course of that era).
The real beauty of that DAC would not be fully realised with the USB port. You should see a big improvement going to an asynchronous USB-SPDIF device like Wavelink HS, or Berkeley Alpha USB which also support Integer/Direct Mode with AudirvanaPlus on the Mac platform, and hooking the SPDIF to the coax/AES input on the EMM Labs DAC2.
You will find a marked improvement too if you use a dedicated computer that runs without the multiple processes running in the background. You will also find that stuff that improves hifi components (power supplies/vibrations) will also have an effect on your PC audio. There are linear power supplies, Solid State drives (no vibrations) that can be used on modified or custom built PCs/Macs.
That said, I find that spinning a disc still sounds marginally better than computer audio but with the leaps and bounds of computer software and technology, it's much closer today than it ever was.