I don’t know if you mentioned this, but do you have your own Router?
I have an AT&T Modem/Router, but I also use my own Router to hook up to the AT&T Modem/Router.
And so my home network (Yamaha, HTPC, etc.) is hooked up to my own Router.
So when the Internet is down (ice storm), my Local Network (Router) is still up for Yamaha AV controller, MusicCast, HTPC server for Kodi.