Servers: Are we there yet?

Exactly; you need a functioning router so the wireless controller(e.g. ipad, android tablet or phone) using the control software can access the server.

Psag, to play music stored on a local drive connected physically to a one box renderer or stored a NAS(e.g. Synology, Qnap, WD MyCloud, etc.) connected by ethernet or wifi to the router you don't need your Internet Service Provider's system to be running. That only matters when you want to listen to Tidal, Qobuz etc. 
Wifi Routers are pretty reliable and inexpensive vs. other gear in this equation. Cheers,
Spencer

True, the system would probably work fine without internet, at least until the lack of internet updates started to affect performance.

Why lack of internet updates should affect performance?  Performance is always the same if nothing is changing.

Yeah, as a veteran in the software/cyber industry it is my experience that MOST software sucks, so I am not surprised at this in a music server. 
...However, you might do some discovery work here: The server has at least one IP address (wireless and/or Ethernet), have you tried accessing it directly via a web browser? (As in http://?.?.?.?  ...where ?.?.?.? is the 4 octet server address.) The server may express its service management through a web server that you could navigate.

@djohnson54 @sbank @psag I say this as a cyber security guy: Devices that allow connectivity to and from the Internet (actually ANY network) represent a danger to other devices in your network that will subsequently develop a trust relationship with said Internet-connecting device.
You absolutely need to understand that your home network now has devices in it that run software that came from whom?That is just a simple fact today and alone it should not stop you from using them, but you need to mitigate against those mechanisms being insecure (who wrote the server code, who configured it?). Think of these devices as requiring constant immunization otherwise every other device might also get infected...
What to do? You have several strategies, at minimum you need to lock down your Internet facing router and perhaps add a second device (such as a firewall) between the server and the router. That acts as a second level of defense against door-rattlers, knob-turners and server-probers who are sitting in their moms basement on their junior high laptop.
The reason for all that above is two fold: First, create awareness that IP devices are dangerous to your home network if they are insecure; Second, to complain at how poorly such devices generally are configured and that if the vendor gets enough calls from us they might do device security better.
QUESTION: Has anyone seen ANY penetration analysis results for any of these music servers?