@DrEHF,
Assuming the Sub is not cabled to the LAN and the fact that the Sub connects to the master Amp in the HT setup over an ad-hoc 5Ghz ‘direct’ wireless connection, the first obvious questions are…

• Has the master Amp WiFi adapter been disabled (if it is wired to the LAN?)
• Is the Sub in the same physical room as the Amp, so as to clearly communicate over a 5Ghz wireless connection?

… or are the products wired to the LAN? If that is the case, are they wired to the same switch or direct to the router?

Firstly, to clarify your setup, you say the Amps are wired, but Subs are on WiFi.

Unless you have disabled WiFi on each of the wired Sonos devices, the Subs should be connecting over SonosNet.

Regarding the missing Sub, I suspect the issue relates to some form of WiFi interference.

Is there anything near the Sub that could cause interference?

See the support page Reduce wireless interference

That ? is a strong indicator to me of at least one potential issue that may not have been touched on by Ken’s answer above. (Edit: or Mr. T’s answer)

There’s a possibility that it’s getting a “duplicate” IP from your router, through the speaker the Sub is trying to “bond” to.

You weren’t specific when you said “I’ve power-cycled everything” as to whether “everything” included the router. I’d certainly try a reboot while all of the Sonos devices are powered down, just to ensure there’s no possibility of a duplication there.  Fresh OS/Firmware loads across the board wouldn’t hurt. 

Thank you all for your responses.  As my living room happens to have wired ethernet jack in exactly the right spot, I decided to connect the Sub via wired ethernet and that has fixed the issue (this still required factory reseting the Sub, and power cycling the Living Room Amps).  That being said I don’t believe the issue is WiFI interference (running a packet test shows no dropped packets and 500mbps from my phone to my router, limited by my phone). Clearly  something more subtle is going on that perhaps I will debug some day.  Thanks again for all your suggestions. 

Perhaps just keep a close watch on the chosen setup as I think you ‘might’ (possibly) go onto encounter some ‘sync’ issues between the Amp speakers and the Sub audio output, perhaps due to network latency, that’s if the Amp/Sub are not wired direct to the same switch back to the router, or direct to the router itself, but that’s really a case of seeing how things go.

I personally prefer a 5Ghz ad-hoc direct wireless link between the Sub and Amp, ideally located in the same room, rather than wiring the Sub, but if it is working with no latency issues, then of course just leave as is and I hope you don’t encounter a problem with the wired setup .. it may actually prove be the best option, as I see you have your Amps in a ‘server room’ which I assume means there are walls/rooms between the Amp and Sub in this instance?

Thanks Ken.  I’m not too worried about latency. The Sub and the Amps for the room are on the same gigabit ethernet switch, and even if it went through my router (which it doesn’t) latency would still be very respectable, as I can ping the Subs and the Amps from my desktop computer (which is on a different subnet) and get 0.4ms ping times . 

Yes, the amps are in my server room (see photo 50 feet from the living room (that being said, I’m still not sure that was my connection issue, as I was having troubles getting the Sub to connect even when I brought the Sub down into my server room!). But as the wired ethernet solution is working well, I think I’m just going to call the matter “resolved”

Thanks again!

Ed

Thanks again,
Ed

Nice setup Ed and lovely dogs too.

I have often seen problems like this when an Amp is in a server room.  Sonos wants to the Amp and Sub to talk to each other by 5GHz direct routing, which this setup frustrates.  Routing over WiFi works badly for this purpose and wiring is often the only solution.

I’m unclear whether the question had been answered as to whether the Amp radios (“WiFi”) had been disabled. In a large wired stack like that it’s not hard to see how that would have happened. 

If the Amp can’t connect its Sub via its own dedicated 5GHz then the Sub has to throw in its lot with any available SonosNet or WiFi signal which happens to be around. This is likely to lead to disconnections.

Surrounds appeared to be connected so I assumed radios still on.

Amp Radios are on.  Anyway, as it’s all working now with wired Ethernet, I'm happy.  

On the wired Amps which do not have satellites (surrounds/Subs) I suggest you disable the radios. Less heat dissipation, less energy wastage.

Moreover there’s less risk of their radios blocking the nearby transceivers of those Amps which do need to communicate wirelessly with their satellites.