Coax Digital Out -> XLR Digital Input cable?

You could also try using Toslink optical since both the Node 2i and Boulder support this.

Toslink direct is usually better than converting coax.

Thank you.

I broke the Toslink flap door already, so I don’t want to use Toslink. 
(I hate this door... too fragile.)

Btw, I thought that Coax is better than Toslink (even better than Glass Toslink cable.)
https://www.whathifi.com/advice/coaxial-vs-optical-vs-hdmi-which-is-the-best-audio-connection-to-use

It turns out I need the converter to use AES input.
I’ll order this converter to use a RCA cable (75ohm).

I'm curious why you aren't using the built in streaming support in the Boulder instead of using the Node 2i?

Long story short, Apple doesn’t allow Boulder to use Airplay (though it’s capable.) And Boulder doesn’t support Idagio Streaming that I use.

To use Boulder streaming support, I need both Qobuz and Roon with Roon Core. I do not want any of these.

For most of music I listen to, the SQ is CD. The rest of quality is slightly better than CD. A little bit of upsampling doesn’t give me any noticeable difference. So, music source is CD quality, and the easiest way to stream music is using Node 2i streamer that has both Airplay and Idagio Streaming.