** EDIT - That RDL piece doesn't have an amplifier in it, so this all goes out the window. It's a line level output. **

This would be tricky since you don't have any real control... the only thing I can think of is if all 4 ZonePlayers are in the same spot, you could wire each speaker through an Altronix DPDT relay. (1 relay for each pair of speakers).

On the normally closed side you wire speaker + and - from the Sonos. On the normally open side you wire output + and - from the RDL piece. (You would have to jump from one speaker to the next for this part of it). Then you would wire the "control out" of the RDL to the trigger in of each relay.

Doorbell is pressed, 12v triggers relays to switch speakers to be wired to RDL instead of Sonos, then RDL plays chime. Chime ends and 12v is lost so speakers go back to Sonos.

A couple things I'm not sure about:
- I couldn't figure out how the RDL would deal with having eight 8 ohm speakers paralleled into it. **and this is the point where I realized the RDL only has a line level out. It has to be placed in BETWEEN a source and amplifier. You couldn't use this with a ZP120. You would have to use ZP90's and put one in between each zoneplayer and its accompanying amplifier...