I wouldn’t worry too much about the RCA interconnects at this point. I think you’d get more out getting a new DAC, a linear power supply for the Node, and using a Wi-Fi extender or Mesh system so you can run an Ethernet cable from that to the Node. Each one of these will probably yield nice improvements, and they’d be additive as you implement more of them.
I’ll just add that you’re using older midFi components including an AVR that will limit the extent to which you’ll hear the benefits of the above upgrades. Personally I wouldn’t throw too much $$$ into this and would focus rather on upgrading your components if you’re really looking for better sound. Otherwise, just sit back and enjoy what you have. Just my $0.02 FWIW.