Idea and code derived from https://github.com/stormboy/node-pioneer-avr - full credit goes there. I have been using avr pioneer for long time but upgrade to Rotel A14 lately which I wanted to control in a similiar way.
Commands available here: https://www.rotel.com/sites/default/files/product/rs232/A12-A14%20Protocol.pdf
Directly copy and paste into iobroker - adjust IP and run the script. Values can be set. Input values: Write without trailing "!". This is added in the script. Volume is at 50 max. Change script as needed.