Denon and Marantz will add HDMI 2.1 to these older receivers for $600

$3,999Last year Denon and Marantz added HDMI 2.1 to their receivers for the first time, and while it added many new features, there's a glitch with 120Hz/4K gameplay on Xbox Series X that requires some extra hardware to make everything work. But what about people with receivers older than that?...