OpenWRT also got it packaged. So a solid and easy way to run it is to just throw the client on some old routers with OpenWRT support, connected to $20 USB DACs with S/PDIF.
Yes, you wouldn't get this running on an existing smart speaker (without first rooting it and some serious hacking).
If you'r in the Apple ecosystem and are using AirPlay with your smart speaker(s), it's however possible to also play synchronized audio across to your own DIY speaker setup, using another open source project.
Or you could of course choose to only use your old dumb speakers with this, and they will pop up as easily selectable sound output devices on all Apple devices connected to your network.
Or combine it (and librespot[2], owntone[3]...) with Snapcast to create a virtual speaker for your whole house that shows up everywhere.
Yes. If you’ve bought a consumer router, and not an “access point”, it will likely have a Ethernet port labeled WAN. Due to this label, the OpenWRT profile for this model will most likely also set up this port as a WAN port for you by default (where it requests DHCP from somewhere and applies NAT and some basic firewall rules). Just delete this interface, and make the LAN network also span the WAN port. Then disable DHCP and IPv6 RA on the LAN interface. Your router is now a dumb “access point”.
You could also make the OpenWRT router connect trough your phone’s hotspot feature temporarily, while you set up your primary connection. Three clicks in the GUI is all that’s needed to join a wireless network for WAN connectivity.
https://www.behringer.com/product.html?modelCode=P0484