thanks a lot, @maxmaximax .
Your widget is working well on my Openhab 3.4 but the best thing is, it inspired me to look into how the Surround Modes can actually be controlled via openhab.
The way to do this, is to activate the “Show Advanced” in the channel list of the Denon AVR’s thing and link an item to the “Send a Custom Command” channel.
For an example, the following commands work for me, on the Denon AVR-X4500H.
MSSTEREO=Stereo
MSDOLBY DIGITAL=Dolby Surround
MSDTS SURROUND=DTS Surround
MSAURO2DSURR=Auro-2D Surround
MSMCH STEREO=Multi Ch Stereo
MSROCK ARENA=Rock Arena
MSJAZZ CLUB=Jazz Club
MSMATRIX=Matrix
MSMOVIE=MOVIE
MSMUSIC=MUSIC
MSDIRECT=DIRECT
MSAUTO=AUTO
The commands are picked up from the control reference sheet found with Google Search.