Digital Coax, optical, or RCA for use with my Bluesound Node player?

I'm very happy with an Audio Envy digital coax from my Node 2i into the dac in my Marantz 8005 SACD.

If you're streaming over 96kHz then I'd stop using the optical and move to digital connection.  There can be a bandwidth limitation with optical cables.  

You'll do a lot better with a 75ohm digital coax vs. RCA interconnect. What is your budget?

I've auditioned quite a few. Acoustic Zen was very good.
Cerious Technologies makes a good S/PDIF cable with a return policy.
BTW, the recommended length for digital coax is 1.5 meters. 

I picked up a Audioquest Carbon digital coax

Analysis Plus "Digital Crystal" COAX 1.5M

Continuous Cast Copper (solo crystal copper) braids, hollow oval design. Demo’d and owned various AQ, AP, Cardas in 1m and 1.5m and preferred AP Digital Crystal. Pricey, but this to a good DAC and wallah!  https://analysis.plus/product/digital-crystal/