Advice for RCA Interconnect Upgrade?

Take a serious look at Wireworld. I have all Wireworld silver eclipse 8 XLR and RAC cables. Plus all Wireworld power cables. I learned to stop mix and matching cables. I started to upgrade my second system to these as well, the nice thing is I have them now so I can try them on the other system and hear the difference. I had a startle 8 red cable from my CD transfer to the dac, and swapped in the sliver eclipse8 and the difference was huge. All the shrill from the Norah Jones CD was now gone, rounded off is you will. The clarity and articulation is more pronounced.

I little work on your room can go a long way to “Taming” your room. 

My wireworld silver experience is opposite. Not a RCA connection but I used a hdmi between cd transport and dac and it hurt my ears so bad I thought I was having hearing problems, way too shrill to my ears. Silver has become an issue in my room layout. 

 You have good gear.  Put the $600 towards upgraded speakers. That will give you a much more audible improvement than a $600 interconnect cable ever will. Much more than a $6000 interconnect. $600 towards room treatment will also be a much more effective way of improving sound. Good luck.

I would try Cardas Clear Reflection. They are warm.