how hook up bluesound node 2 to external dac

All you need to connect to an external dac is a digital coax cable.  The analog and digital output are active at the same time from the Node.  So you can run the analog outs from the Node to one of your preamp inputs.  Run the coax to your dac and connect the dac to another preamp input.  Now you can compare the sound of your external dac to the Nodes internal dac by just switching source inputs on your preamp.  Some volume compensation may be necessary.

Got everything sorted, now just experimenting what options are available.  One more question is cables, which one is is your best experience.  In my system cables really do make a difference. 

Mike 

There is no USB out on the Bluesound node2
Coax or optical.

Coaxial or optical? 

Try both, I prefer coaxial in my system.