Different systems playing same music simultaneously

I have four different systems located in different rooms.
Is there a way to make them play the same music like a multi-room system?
Could I send the signal from one source to all the systems at the same time?
Each system has its own amplifier and speakers.
Is bluetooth an option? Can I use a transmitter and several receivers?
Does anyone have this kind of setup?
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Bluesound is probably what you want. 
A set of Nodes- and they don't have to be the latest edition, will give you what you want as a very competitive price.
It is what I am using as I write...

Depend on setup.
If all analog signals means running lots of long runs of cables and a multi out box, can be done but it's work.
Networking as Audiotroy states is better option.
But all depends what you have in your systems.
Guys we sell the Blue Sound products which are fantastic, however, only Roon gives you the ability to talk to many different devices,  so through Roon you can talk to Sonos, Google Chromecasts, Naim Muso, Naim  Uniti products, Auralic, and many, many others.

Blue Sound's Node is a very good $550 streamer, however, a high end Roon server coupled to a good Dac will sound even better.

Dave and Troy
Audio Doctor NJ
I am using a Dayton Audio wave link 2.4 GHz wireless transmitter/receiver to send signals from my music room to a second system in my kitchen.  Bought from Parts Express.  Cost about $60.00.  Works great but there are certain limitations.  You'll need an output from the preamp and assuming you are sending an output to your amp you'll need a second pre output.  Tape out could work or maybe headphone out.  Transmitter and receiver work best with line of sight between the two.  Call Parts Express with your questions.  

This is pretty easy with Chromecast groups. The Creation 5 control point also does it with diverse renderers, but Chromecast is much more reliable.