What Digital to Digital Converter Do You Use? Why?

i have a CEDAR DCX and CRX [declicker/decrackler] which are digital-only devices, and to get analog sound through them in the process of digitizing old phonograph recordings, i use a Phillips ISP a/d converter to put it through the CEDAR pair, then a Mission d/a to convert back into analog for recording onto a Tascam SD recorder so i can put them onto my hard drive for further editing. 

I use a Matrix X SPDIF 2 between my Innous Zenith MKII streamer and PS Audio Direct Stream DAC.  For I2S, I use a .7 meter Wireworld Platinum Starlight 8 HDMI cable.  I get a very noticeable SQ improvement via I2S as opposed to USB from the Zenith directly to the DAC.  

I'm sure there are better DDC converters than the Matrix, but I'm quite satisfied with it in my system.

I purchased the Denafrips Iris DDC (installing later this week), but I will be outputting to a Denafrips Pontus II DAC.....which has configurable I2S inputs as well. If you're considering the Iris to the Holo Audio, I'd reach out to Alvin Chee of Vinshine to check on compatibiltiy

According to the designer the USB input on the Holo May is the preferred one so try it until the DAC is broken in.  I have both a May KTE and a Spring 3 KTE and I concur with the designer and see no need personally for a DDC.  Your money though if you have an itch. I would and was more interested in finding the right USB cable.