Hi guys, connecting the radio transmitter to the analogue output works.

Not directly, Sonos Connect has no radio output.
There is certainly a workaround via bluetooth connector, delay may be available.

Good day.
Yes, Advance Paris has a product that sends a Bluetooth signal, you can connect it to the Sonos at the out and single goes wireless to the active speaker.
You can order it at Best Hi Fi in Zurich.
Have fun