I just fell foul of Sonos obsoleting support for (re)adding new speakers in the desktop app, and only supporting it for the Android app. Even the Android support only works if you are using what they deem a modern enough version of Android.
In my opinion, removing such basic features and forcing people to go out and buy a new phone so they can (maybe) continue using their already very expensive system they've had for years is very shabby. I'm also sure there are some people who don't have and don't want a smart phone at all.
As I am a miser and an engineer, I devised the following procedure that didn't require me to go out and spend $1000 on the latest iPhone. Unfortunately, the procedure requires a bit of time and, if you are not familiar with concepts like "virtual machines" maybe a bit of self education.
i) Install Oracle virtualbox https://www.virtualbox.org/
on your PC or laptop. Versions are available for Windows, Mac OSX and Linux
- Check that your PC/laptop supports virtualization, and that it is enabled in the BIOS.
ii) Follow the general procedure described in https://www.howtogeek.com/164570/how-to-install-android-in-virtualbox/
to install an android virtual machine.
- Configure the Android virtual machine to use bridged networking (e.g. bridge the wireless adaptor on your PC)
- it is necessary to use Android > 5 to have the add speaker functionality. I used android-x86-7.1-r2.iso
iii) Install the sonos controller app in the virtual machine.
- You should now have the ability to (re)add your speakers from the settings menu.