If you are talking about PC control over your Denon receivers and DVD, then you would want a dedicated serial cable (store bought, or fashioned from Cat5 wire w/ adapters on both ends) between PC and Denon. this is NOT an ethernet (PC LAN) cable, but can by same type of wire (Cat5).
If you are remote between the two, then you can put an ethernet to serial adapter (like a globalcache or Lantronix MSS100) on the PC network and plug the serial side into the Denon. the GlobalCache some support two serial ports so only one LAN wire between PC and GlobalCache.
You can even do wireless, but not recommended for reliability.
From a software side, MainLobby supports all of the Denon Rs232 receivers. Can't remember if the DVD player is supported today or not.