DAC Suggestions for Aurender N100C

Suggestions for DACs that match well with the Aurender N100C (basic N100 with coaxial option).  I have mine matched up with a Schiit Audio Gumby.  The overall sound is good, though there is often a graininess that is an issue.  I exchanged my first Aurender (thanks Music Direct), but the problem persists.  I've used USB and Coaxial.  Now I'm wondering if it is the synergy (or lack there of) with the Gumby.