The 3600 and 4500 probably measure close while the 4700 8K HDMI is a first rev. It looks like using the optical when possible will improve the SINAD.
But Denon won't increase 4700 sales with reviews ending with... "Anyway, I am so unhappy with the state of product development in these companies and despite some good traits, I cannot recommend the Denon AVR-X4700H."