If you are willing to accept something obscure PulseAudio actually has the best thing. Look into the PulseAudio native module which just let’s you put a speaker on the network as a normal boring sound output that works as if it was connected to your computer.

- Install the zeroconf module on both server and clients.

- Enable the native module on the server and open the port and tell PA to publish an mDNS record.

- See the speaker just appear in your sound options. Play!

Actual instructions if you want to set it up https://blogs.gnome.org/ignatenko/2015/07/31/how-to-set-up-n...