I assume you’re currently using the S1 App and trying to add ALL to that App as your online community profile shows that you have a Play:5 (gen1), which is S1 compatible only.
Firstly if any of your ‘other’ Sonos products have ever been setup using the Sonos (S2) App, then to add them to an S1 system, you first will need to downgrade them - see this link which explains how to go about doing that (if required) -
https://support.sonos.com/en-us/article/downgrade-a-sonos-product-to-s1
Start the setup of the S1 system initially with the Play:5 then downgrade/add the other ‘reset’ products (as required) using the S1 App.
You only need downgrade any previously upgraded products (obviously) and after completing that step you can go onto add them to the S1 App.
An alternative, is to setup/use the Play:5 (gen1) on an S1 system and to separately run all your ‘other’ Sonos products on the new Sonos App (S2).. my suggestion there is to setup the Play:5 (gen1) first in the S1 App and when you’ve finished doing that power off the speaker and then go onto install the Sonos App (S2) and reset/setup your other devices within that App, but note these ‘other’ Sonos devices behave as a separate system and so cannot be grouped/play with the Play: 5 (gen1). How you choose to set them up/configure the speakers, is really a matter for you, but all your products apart from the Play:5 (gen1) are compatible with the new Sonos App.
When all are setup in the new Sonos App you can power on your Play:5 again and use each Sonos App to separately control your S1/S2 systems.
Hope the link and info. above assists.
The below link explains how to factory reset your products (as/if required)…
https://support.sonos.com/en-us/article/reset-your-sonos-product
The reason that iTunes does not see your Sonos speakers by the way is that App connects to AirPlay & Bluetooth speakers and the Sonos devices you have are not compatible with those connection methods, but you could perhaps wire the Play:5 (Gen1) line-in to your PC/Mobile and play your music to the speaker over an analog line-out connection.
Note: If you want the Play:5 (gen1) line-in audio to play on your ‘other’ Sonos products then you will need to setup ALL in your S1 App only.
My speakers are old school, only work on S1, never have they been able to connect to the newer app.
Everything was working fine - all speakers showing up in my S1 app as well as iTunes, until someone disconnected them to set up a new tv for me. Now nothing is working properly. It makes no sense. Again, I’ve reset & factory reset tons of times. I get random times of some success (some speakers show up sometimes but then disappear and cannot be found again). But mostly it’s just a mess.
Are there “Sonos installers” I can get to come try to figure this out? I’m losing my mind with this.
Factory Resets are a sure way to drive yourself batty, worse they rarely fix anything permanently. As Sonos support suggests, avoid them unless support or a knowledgeable member suggests doing one.
If all your Sonos and Controllers are still on S1 recovering (what the resets didn't destroy) should be simple.
I'd start by unplugging all but one Sonos, one that can be wired to Ethernet and your router.
Reboot your Controller.
Do a Factory Reset of that Sonos and follow the steps to set up a new system.
If you have issues then try connecting it by Ethernet to your main router and try again.
If that works, check for updates.
Confirm it is working well.
Power up one more Sonos, Factory Reset it and follow the Add to System instructions in the controller.
Add the rest one at a time until all are present.
Sonos offers phone support that is usually pretty good.
Local audio dealers may have Sonos installers, make sure to mention S1 to them.
The solution, for those interested. It was the ROUTER. Resetting the router and a factory reboot of each speaker allowed them all to finally show up.
