The Zenith Mk3 USB output is noisy. You don't know what you are missing until you place a very good DDC on the USB output of the Zenith. I am using an Audio-GD DI20 HE, and the difference in quality is outstanding with the DDC.
For those that have separate Streamers & DACS
What are some of your favorite streamers/servers strictly from a sound quality perspective? Please assume a stand-alone DAC. I've read such a variety of opinions on streamers and was interested in opinions from those that have tried different streamers on with their DACs.