On this project I have build a simple control panel for my Denon AVR (AVR-X4100W).
Most of Denon A/V Receivers are network ready, so you can control them within a web interphase or an app. There is no official documentation for the HTTP API (there is an official telnet api), but it is easy to get the calls with a tool like Wireshark. I use these HTTP calls to remote control the Denon AVR with an Arduino and Ethernet shield. My arduino control panel can power ON/Off the Denon and control the volume with a rotary encoder.
For this project you need:
Load the code to the Arduino.
On the code you need to set the IP address of your Denon avr (variables denonIP): char denonIP[ ] = "192.168.2.126"; //set the IP of your denon