Who is using I2S cables?

Well, sadly there is no ‘standard’ established for i2S resulting in manufacturers using both RJ45 and HDMI connectors. This has also lead to some compatibility issues (handshake) between components from different manufacturers. As far as I know there is no designated or specialized cable for i2S yet, you can use any good quality HDMI or Ethernet (RJ45) cable for i2S connectivity.

I waited long enough for this conflict to settle down and recently pulled a trigger on a DAC/streamer that connects directly to my Ethernet network via standard RJ45 LAN connector, thus eliminating the need for any external cabling (i2S, USB, SPDIF, AES/EBU) between the DAC and streamer or server.

The i2s connection used between boxes is a buffered version of the internal i2s signals. As @lalitk mentioned, there is no standard for the pinout, so you need to make sure the two devices you are connecting use the same conventions.

Some DAC manufacturers, such as the Denafrips DAC I am using, have a programmable interface that allows the interface to be configured to work with different conventions. 

The advantage of i2s over other synchronous digital interfaces (SPDIF, AES, toslink) is that the clocks are separated from the data.

I am using i2s between my Denafrips Gaia DDC and Denafrips Terminator Plus DAC. I found this interface to be a very noticeable upgrade from using AES, even when using a very inexpensive HDMI cable. 

There are audio cable vendors that are designing cables specifically for i2s. Whether they are better than a good HDMI video or Ethernet cable, I can't say as I haven't done a lot of comparisons. 

I am using a Tubulus Argentus cable based on recommendations from other users. I found that this cable provided a subtle improvement over the $12 HDMI cable I bought from Amazon, but no where near as big an improvement than switching from AES to i2s in the first place. 

Currently running an I2S between PS Audio cd and dac. To these ears it sounds superior to the xlr or coaxial connections. The I2S cable in service was the one provided with the unit from ps audio.

I have a Jay’s Audio CD transport and DAC and use an AQ cable for the i2s and it works well.

Thank you @jaytor . And yes, I understand a little bit re. the different configurations @lalitk mentioned. Which is why I was asking for smarter folks recommendations :-) 

If I read correctly, you noticed a significant improvement from AES to a $480.00 I2S cable https://www.highendcableshop.com/product-category/i2s-cables/ ?

So, two follow up questions: 

1. any chance you had an "A-B" experience with a high quality USB A to B connection and is the upgrade expense that big an improvement? 

2. re. a properly configured high end HDMI vs. the Tubulus Argentus I2S, you could tell a significant -- i.e., it was worth it -- improvement? 

Thanks much!