How to output sound from several devices to the audio system at the same time?

Question

Audio

There is a 5.1 audio system, two laptops, one large computer, two smartphones.
It is required to connect all this at the same time to the audio system.
Question: how?
Googled on the topic of mixers, wireless external audio cards and didn’t find anything sensible.
Ideally, you want all this to work over a local network. While I'm thinking of buying a raspberry and an external usb audio card for it. Use Malinka as a sound receiver from different devices and an audio mixer. But maybe there are easier ways?

Answer 1

It is simpler to solder a simple mixer from several identical resistors (approximately several kilo-ohms each) to each of the 6 inputs of the audio system - as many as signals will be sent to this input. On the main stereo channels - five each, on the rest - three each (from laptops and desktop, because the mobile phone does not give 5.1).
The 1k ohm resistors in this picture are such a mixer (4.7k ohm regulators are not necessary, they are only needed if you want to adjust the signal ratio).
Of course, such mixers will dampen the signal, but I hope there is a margin for gain.