@rolee910 and you'd be right.
The best connection is a digital out from the Esoteric K 05X into the corresponding digital input on the Esoteric N 05XD
The most stable of those connections is going to be the USB B connection as that carries the most data outside up to 32bit and up to 384kHz sample rate for Linear PCM formats and up to 22.5MHz for DSD formats so all your SACD and CD needs are more than covered.
So you need an USB B to USB B interconnect. I assume they shipped with some