You would need to direct the line in to play on the ‘room’ that is the PLAY:3s.

Be aware there’s a minimum of a 75ms delay on a Sonos analog line in, such as on the CONNECT:AMP, so it may be difficult to get any lip sync with the projector’s video. 

This is why the ZP 120 /CONNECT:AMP was never sold as a home theater option. Sonos made their soundbars for that use case. 

Thanks. Direct Line means that I connect the projector via RCA to ConnectAmp which is in the same "room" than the play3s?

Thanks for delay note

No, CONNECT and PLAY”3 will be separate Rooms. Rooms can be Grouped to play the same source. While the Grouped Rooms will be time aligned with each other, there will be a 75ms offset from the projector’s output. Both CONNECT and the PLAY:3’s will be stereo, not surround.

House rooms and Sonos Rooms are always confusing.

A Sonos Room is one or more Sonos devices, and is shown as one entry in the Controller. A Sonos Room can be one Sonos, a Stereo Pair, or a Home Theater set, plus a Sub or mini-Sub.