Sonos does not make a single device that can connect 10-12 speakers. Each “room” will need an Amp if you intend to have different music playing in each. You can purchase a multi channel amp with enough channels for each room and add a Sonos Port as the audio source. All rooms will play the same audio unless the amp has multiple inputs as well.

Depending on your use an external amplifier with the needed number of outputs to drive your speakers (as above) and one or more inputs you could connect Sonos Ports to might be your best solution.

Each Port can provide one stream of music so it you wanted to listen to something different in two rooms you’d need two Ports and two inputs to the amp. Many multi-channel amps have nice switching options.

Take a look at a couple here to get an idea what is available.

https://www.crutchfield.com/shopsearch/multi_zone_amplifier.html

It is very unusual to use coax cable as speaker wire. Coax is usually run to an electronics gadget of some sort that may be connected to a speaker. Have you verified that there is one wire per speaker at the central location? Have you verified that coaxial wire is connected to each speaker? Are there any signs of electronics scattered about that could operate speakers? There could be remote Volume controls or some sort of keypad in each room. What kind of connections are used at the end of each coax at the central location?

At this point we cannot assume that this is or was a competent installation. There are a lot of weird ideas out there. If the system was a few decades old, its design will be very different when compared with more modern approaches. Decades ago multi-room systems were on the edge and required some imagination to implement.

Consider the possibility that the coax is connected to cable jacks, not speakers. If this is the case, there will be speaker wires or jacks scattered about.

As a crude test, connect a flashlight cell to one of the central coax cables. If the other end is connected to a speaker, there will be a “thump” from the speaker at the instant of connection. Connect one end of the battery to the inner coax wire and the other end of the battery to the outer metal shield. You’ll need an assistant to perform this test. If you get a “thump”, label the wire and continue with the others.

Consider calling in an expert friend or hiring a pro to sort things out. Take care when selecting that “expert” friend. Many self declared experts are actually hazards.

That BELDEN 1841A is an odd choice for speaker wire — if it is used as the speaker wire.

I tried following the wires, a lot of them disappear into the walls, but there are many coax ports and loose wires coming out of the walls-- I’m guessing they had portable ground speakers connected to them.

The thump test did not produce anything. I am going to continue to investigate further. Thanks for your help

If there are speaker wires or jacks, thump these.