Denon, YamahaAVR drivers have been updated. A PioneerAVR driver has been released. PioneerAVR is an experiment. Let me know if it works. The goal of these drivers is to provide the basic functionality for day to day use. They can be added to if necessary. The volume UP and DOWN commands implement the protocol commands for up and down which increment in 0.5 db steps.
All three drivers introduce a volume_db variable that tracks the db values while the volume variable continues to track percentage.
The volume slider web component has been modified to allow for using the db label variable on the slider thumb instead of showing percentage. Look at the individual driver pages in command builder pages to see how to implement.
Here is the Denon driver showing the db variable being used.
Here is the web object being edited in the Designer showing the new Thumb label variable.