How to connect outdoor projector to amplifier

Hello guys,

i am thinking of installing an outdoor Projector, but i am skeptical on some issues and i need your input please!

I have already outdoor speakers. These are connected to an amplifier in my kitchen area.

If i install an outdoor projector, it would be perfect to use these speakers as well. But i am not sure what kind of cable i can use to connect the projector to the amplifier, in order to transmit the audio from there to the outdoor speakers.
My amplifier has inputs (AUX, Tuner etc) and i can pass through the pipes another speaker cable to connect the projector. But is it possible to create a Stereo Audio connection with just speaker wire?
Is there another way that i can make this possible? Can i make it over ethernet?
I am sure the answer is pretty straight forwarwrd, since a lot of houses have provisions for outdoor projectors, but i still cant find this answer!

I found some articles indicating that long RCA or COAX cables can be used, thus i suppose this is an option.
But for RCA cable can i cut the ends so to put them through the pipes, and then connect them again?
Are there any reccomendations please as to which one exactly should i use RCA or COAX?

Thanks!