I think most of us agree the new Sonos (v80) app is lacking key features that were on the prior version.

After some trial & error I was able to get the prior S2 (Gold) app reinstalled because I had a manual backup of my iPhone on my computer.

The steps I used were:

1. Make sure your manual backup was done before the new (v 80, black) Sonos app was installed on your device;
2. Erase your iPad/iPhone and perform a restore from the backup that’s on your PC;
3. Once the device restarts for the first time you need to immediately disable auto updates and downloads for apps (Settings, App Store). This is an important step otherwise you’ll get the new app installed again..
4. Let your device complete the app installs.

The process took about an hour but I’m happy now that I got the prior S2 app reinstalled.. 

Good luck.