I2S Recommendation

What input best depends on how well each interface optimized. The Harmony usb interface nothing special so its very possible I2S will provide superior sound quality. In my case I was using Sonore OpticalRendu with Audioquest Diamond usb with Harmony at first. Later went to OpticalRendu feeding Denafrips Gaia usb, Gaia to Harmony via  .5m*Tubulus Ximius, Harmony sync'd to Gaia's superior I2S clock. 

To really take advantage of I2S potential, one should have highest quality OXCO clock in streamer or DDC vs dac internal clock, so superior timing via syncing to the external clock. Also keep I2S cable short .5M or less, longer cables throw off timing defeating much of the advantage of the external clock. 

While the Harmony was nice enough via usb, going this particular I2S route really upped the game, greater resolution, transparency along with more analog like presentation.

I tried a very short 6" long I2S (HDMI plug) cable- no name and bought the DH Labs 2.1- the extra length of the DH Labs certainly didn’t make it worse- 1/2 meter. 

The question is will your DAC work (or is the I2S input user configurable) with whatever the digital source is (and same questions re compatibility/configurable). *(One spec I read said your DAC is 8X auto configurable so I assume this means you should not have an issue but you are no doubt aware that no one standard exists for how these devices are wired for I2s). 

I bought a DDC to get around the problem since my I2s source component was not compatible with my DAC. The DDC was directly compatible with the DAC- same manufacturer-Gustard-though it does have the ability to reconfigure with some limited options and if I recall, a promise to add more options via field programmable chip. 

I think this digital front end (which enabled me to eliminate the Mac mini and Audirvana), though very modest, sounds terrific using the I2S over a very good, well tuned system and I’m all about old LP pressings in top condition. In other words, I’m fairly critical. I understand why people would go deep into digital especially given the cost of entry into the LP these days, from turntable, arm and cartridge-(the latter being a consumable) to effective record cleaning facilities of some sort, to the cost of pressings, particularly OGs of desirable records in top playing condition. If I were to start today, I don’t know that I’d dive into vinyl- but I started so long ago, and have a considerable record collection, so use both for access to more music.

I’m using a simple device that can play from an SSD through a variety of outputs at high resolutions. Much depends on the source material-some redbook standard files sound terrific, others less so, but some of the higher res DSD and high rate PCM are great too. I’m good where I am on the digital front now that I have this set up w/ I2S and I’d say 85% of my listening is still the LP. Nonetheless a big improvement, less artificial sounding to my ears on my system. 

Another happy micro Dac user here.  I tried two inexpensive HDMI cables, including the AudioQuest LGC directional HDMI, but was disappointed with the sound. Then I tested the DH Labs HDMI 2.1 cable and ended up liking/keeping it—especially after burn-in. It delivered a fuller, bassier sound than the AQ. According to Greg from DH Labs, their HDMI cables take about 40 hours to fully burn in. Also, be sure to get the 2.1 version rather than 2.0—it uses lower dielectric insulation, which reduces signal degradation and lowers capacitance for better overall performance.

Congrats on your nice new DAC.  I use this and it sounds so good I haven’t bothered to upgrade yet.  At about 7 bucks it’s a way for you to assess i2S vs. SPDIF without risking a lot of $ (my cable is 6” long but now only available from 1 foot on up). 

https://www.monoprice.com/product?p_id=24182

This one looks interesting to me and some people here have had positive comments I’d you’re up for spending $99.

https://wyred4sound.com/products/hdmi-pcocc-premium

This DH Labs cable also gets good comments and is a bit pricier.

https://silversonic.com/products/digital-cables/hdmi-2-1/

Just some potential options at a few price points to get started.  If you’re looking for something more I’d look at Wireworld or Tubulus and think I read some good things about Wywires too. Regardless of the cable you want it as short as possible for i2S as it does not travel well and the signal degrades quickly over distance.  Optimally you want 1 foot or less, but get the shortest length you can.  Hope this helps, and best of luck.