WessexPete,
Entirely at your own risk… The easiest way, is to perhaps power-off all your (now) ‘S2-upgraded’ devices and remove the S2 App from your Sonos mobile controller(s), leaving just your Play:5 (Gen1) running in/on the S1 App …and then factory reset your powered off devices and add them back to the S1 system via ‘Add Product’ in ‘Settings/System’.
All being well, they will (hopefully) downgrade on re-install.
Don’t forget to uninstall the S2 App before you start, otherwise you may find you encounter some difficulties …and whatever you do, do not factory reset your Play:5 (gen1) as you may lose your original Household/System Settings etc.
Ken
all make sense will give this a try and advise on the outcome. Greatly appreciate the suggestion.
cheers
Pete