Plugin: add Plugin to music sources

Hi!
Recently I wrote a “Remote Control”-Plugin for Braun Atelier (Hifi, ~35Years Old, with RS232) Devices.
The Control via RS232 works fine.
The only “Problem” is:
The whole UI of my Remote is only accessabale in the Plugin Settings-Menu (Settings/Plugins/installed Plugins/mastercontrol).
I would like to add a “Button” for it to the Music Sources part on the main Page.
Since this Plugin controls the playback of my Hifi-Setup (like sources, power, volume…) it should be accesable in “Music Sources”.

As far as I understand the Index.js provides the configuration for this…But If I add this:

mastercontrol.prototype.addToBrowseSources = function () {
// Use this function to add your music service plugin to music sources
var data = {name: ‘MasterControl’, uri: ‘spotify’,plugin_type:‘miscellanea’,plugin_name:‘mastercontrol’};
this.commandRouter.volumioAddToBrowseSources(data);
};

The Plugin does not appear on Music Sources.
All “Placeholders” bellow that (in example files) seem to be responsible for a playback function, (Play, add to queue, browse sources…) which I do not have and not able to provide.

Where is the Configuration for the music sources UI-Part?
the UIconfig.json seems to be responsible for the “settings” side of the Plugin.

Is my request even Possible?

Best Wishes,

Christoph

PS: I attached the plugin (Setup is not finished…)
mastercontrol.zip (263.8 KB)

Screenshots:
Screenshot Plugin
The desired Position

Volumio Information

Volumio Version: 2.861
Hardware: Pi4/4GB
DAC: HifiBery DAC Plus ADC
USB Serial Adapter: /dev/ttyUSB0