Auralic Aries G2.1 connect to Holo Audio May KTE

I would recommend trying equal quality AES/EBU and USB. Choose what sounds best to you in your system. If I had to guess though it would be USB.

USB according to Holo Audio.  If you used their Red streamer, then an i2S cable. 

I agree with all of the above. One of the features you paid for (and received) with the Holo Audio May is USB implementation that features galvanic isolation and an accurate clock. It has been demonstrated both through independent measurements and subjective listening to deliver noiseless, jitter-free performance, even with noisy sources (e.g. PC).

USB works best between my Holo Audio May KTE DAC and Aurender N200. The May actually has double galvanic isolation. I'm using a DH Labs Mirage cable and it works great.

I have Aurender n20 and tried the coax out to my holo Kte and I heard no  noticeable difference between it and usb.