Pioneeravr binding - volume up/down

Hello@all,
I have a Pioneer XC-HM81 Micro-Hifi-System and use the Pioneer AVR binding (binding-pioneeravr - 2.5.2) for controlling it remotely via network. The command set of this system is very limited, but at least it is possible to control power, mute, volume up/down (no numbers, only VU/VD), source selection via telnet.
With the binding i am able to switch the box on/off and un-/mute. But increase/decrease the volume with the binding fails.

This is my current items-configuration which is working for power and mute. It is also possible to receive the actual volume value, but increasing/decreasing volume won’t work.

//items
Switch   XCHM81_Zone1Power                             "Zone1 power"                               {channel="pioneeravr:ipAvrUnsupported:xchm81:zone1#power"}
Switch   XCHM81_Zone1Mute                              "Zone1 mute"                                {channel="pioneeravr:ipAvrUnsupported:xchm81:zone1#mute"}
Number   XCHM81_Zone1VolumeDb                          "Zone1 volume db"                           {channel="pioneeravr:ipAvrUnsupported:xchm81:zone1#volumeDb"}

In my sitemap I tried following configurations

//sitemap
Switch item=XCHM81_Zone1VolumeDb mappings=[ON="Vol+", OFF="Vol-"]
Switch item=XCHM81_Zone1VolumeDb mappings=[INCREASE="Vol+", DECREASE="Vol-"]
Switch item=XCHM81_Zone1VolumeDb mappings=[UP="Vol+", DOWN="Vol-"]
Setpoint item=XCHM81_Zone1VolumeDb step=1 minValue=-80.5 maxValue=0

Following warning messages are thrown in the Log Viewer after the respective vol+/- buttons are pushed in the basic ui:

[WARN ] [rest.core.internal.item.ItemResource] - Received HTTP POST request at 'items/XCHM81_Zone1VolumeDb' with an invalid status value 'ON'.
[WARN ] [rest.core.internal.item.ItemResource] - Received HTTP POST request at 'items/XCHM81_Zone1VolumeDb' with an invalid status value 'OFF'.

[WARN ] [rest.core.internal.item.ItemResource] - Received HTTP POST request at 'items/XCHM81_Zone1VolumeDb' with an invalid status value 'INCREASE'.
[WARN ] [rest.core.internal.item.ItemResource] - Received HTTP POST request at 'items/XCHM81_Zone1VolumeDb' with an invalid status value 'DECREASE'.

[WARN ] [rest.core.internal.item.ItemResource] - Received HTTP POST request at 'items/XCHM81_Zone1VolumeDb' with an invalid status value 'UP'.
[WARN ] [rest.core.internal.item.ItemResource] - Received HTTP POST request at 'items/XCHM81_Zone1VolumeDb' with an invalid status value 'DOWN'.

[nt.ItemStatePredictedEvent] - XCHM81_Zone1VolumeDb predicted to become -53
[vent.ItemStateChangedEvent] - XCHM81_Zone1VolumeDb changed from -54.0 to -53
[vent.ItemStateChangedEvent] - XCHM81_Zone1VolumeDb changed from -53 to -54.0

Is it actually possible to send the VU/VD commands with this binding version and if so, how can I do this?

Thanks!

P.S.: This has already been posted in PioneerAVR 2.0 issues - #7 by Pipo17