I have created an app for the Homey by Athom to control Marantz AVR’s over ethernet (I have the NR1604 model myself). See https://apps.athom.com/app/nl.marcovandenhout.marantz (version 0.0.1 has been published, 0.0.2 is in review)

This page is meant to provide some generic links and information about the protocol used. Bugs or feature requests for the app itself can be added at https://github.com/hilvarenbeek/nl.marcovandenhout.marantz/issues

PDF with possible commands (written for Denon AVR’s): http://www.awe-europe.com/documents/Control%20Docs/Denon/Archive/AVR3311CI_AVR3311_991_PROTOCOL_V7.1.0.pdf

Found out that Marantz has quite extensive documentation on their own website, for example go to http://us.marantz.com/us/Support/Pages/Manuals.aspx and you can download Excel sheets with the command lists, and also which model supports which command 🙂

Models to add: