After some time of investigation and reseach, I think I have found and implemented a quite nice solution in my IT home network in respect to a multiroom sound and media solution.
I have compiled a few static pages on my home page explaining the details.
In total the complete environment including the web server consists now of three Raspberry Pi 3 B+ devices and one very cute Raspberry Pi Zero W device.
The software is based mainly on max2play.
Check out the details of my multiroom sound and media solution and let me know if I can help you with any setup or recommandation on your side.