That "socket" you are showing is something else. It's an xlr to ethernet adapter. Cat5 cable, with it's 4x twisted pairs is an excellent cable for transmitting balanced audio signals over long distances. One ethernet cable can transmit 4 such signals. The signal running in the ethernet is still the analogue signal though.

So it's quite popular these days do use ethernet cable for long signal runs in live audio installations. Much cheaper than traditional snakes too.

Your second link is a rj45-in-xlr-shell plug. It's used where you need a robust and reliable rj45 connection that can withstand more abuse than a typical "naked" rj45. I think it's fairly popular in industrial computing and military settings. There are various types of plugs that are embedded in an xlr shell for the same robustness reason.

specifically, the first one is XLR to RJ45 - the cable could be cat5, cat6, cat7, etc depending on the standard it was manufactured to. and ethernet is the protocol for the digital signal those cables usually carry.

as you say, it's common to use that cable for long analog audio runs, but when it is used that way it's not ethernet.

Yeah I mostly wanted to show the idea. Very interesting to hear it's used outside PA too. Thanks!