i use the dummy dimmer for setting the volume at my denon avr.
"name": "Denon Master Volume"
then i created a variable that halves the slider value (if slider is at 100% the volume is at 50, so its not possible to set the volume too loud at full slide)
"expression": "round(($denon-volume-slider.dimlevel * 0.5),0)"
well and here’s the rule that sets the volume
IF $denon-volume-slider.dimlevel changes THEN execute "curl -s http://192.168.178.67/goform/formiPhoneAppDirect.xml?MV$denon-mastervolume"
if you like to, you can have a look at the denon avr control for inspiration https://forum.pimatic.org/topic/979/denon-marantz-avr-remote-control
its not a plugin rather a collection of devices and rules. works pretty good for me.