What type of problem would that suggest, or what possible route of correction? I now have two routers in series and I can ping either of the routers from the computers but no computer can ping any of the other computers.
Can you copy files between the computers? If so then this really sounds like a firewall(s) blocking the ping request. Which really isn’t an issue unless you just like pinging your computers or need to troubleshoot your connections.
One thing: The MAC address listed on the back of the Denon is not the same as the MAC address that shows up in the router's device list, whereas the MAC addresses listed in each computer's "ipconfig /all" info is the same as the MAC addresses of the computers listed in the router device list . Not sure what this indicates, perhaps it provides a clue as to what is going wrong
It sounds like you have MAC address filtering enabled which is not a bad thing but will only allow the MAC addresses listed to connect to your router. Can you edit the Denon’s MAC address in the router to match what is actually on it.