Trouble with connecting multiple Amps - Help Needed

Hi guys. i'm new here and I need help with something, I really hope that someone knows how to solve my problem.

Can someone tell me how can I connect 3 amplifiers with each other but I want the music to come from a single source. The problem turned out when I bought 4 more speakers and one more amplifier with 4 Inputs and 4 Outputs. Before I had 2 amps for 4 speakers, and it was simple to connect them. I had a cable from my PC to one of the amps, and then use the other Line Ins of the Amp to connect the other amp. Now the third one, the one with the 4 inputs and outs is the problem.

The first and not so good one ( I know .... ) is this one https://zesilovace.heureka.cz/skytronic-xxl-pro-480/
The second one is http://www.keystonemusic.ca/product/behringer-epq-900-power-amplifier/
And the third and new one is https://www.sweetwater.com/store/detail/EPQ304--behringer-europower-epq304-power-amplifier

So, to simplify I want to connect one input( source of music ) to one amp, and then connect the amps with each other. Is that possible?

Thanks upfront, maybe it sounds lame but i tried every combination, and tried also with a mixer from different outputs, but that doesn't seem right to me.