Digital coax from CD player to DAC, RCA or BNC-RCA?

I've been using my Marantz SA8005 as a DAC feeding a RLD-1 to a recently modified DNA-1. I will be swapping in a Stellar Gain Cell DAC and will try it as a preamp as well. If the synergy isn't there, I have other plans for the SGCD.

That being said, I would like to find a good digital coax and hear that a BNC cable with RCA adapters is a possible option over a cable terminated with RCA.

I've researched some of the topics on graphene but not sure where to start.

Would like to keep this purchase under $400, and I hear 1.5M is where I should be in terms of length at the shortest.

Open to all input and criticism, also feel free to PM me.