I have been using Volumio for some time now and I am very found of it. I have 3 Raspberry Pi with HiFi Berry DAC pro in my big house but also some HiFi equipment with Airplay. I use Spotify but I also have a Tidal account and use Tunein for radio listening. So on my wishlist is Tidal and Tunein for Volumio.
Some weeks ago I tested Logitech Media Server + PiCorePlayer and it worked very well. It gave me a very flexibel multiroom system with all services I wanted. But I liked Volumio GUI better. With Logitech Media Server I can use my Airplay Equipment as player in my multiroom sytem. So I reistalled Volumio on my Raspberry Pi and got booth worlds. Now I can choose to use Volumio localy on one player or I can use all Volumio players together with the other players in my multiroom system using Airplay. It works great.
Hm, your system is really cool!