Whole house audio system

We recently moved into a house remodeled in 2013 to include a whole house audio system with 11 in-ceiling speakers in 5 zones. They’re driven by a standard Yamaha receiver amp, but connected so that 1 channel goes to a splitter which divides the output into 4 zones. 2 speakers (1 zone) looks like they were never connected.

We’re not currently using the system because the receiver is 20 yrs old and has no aux input jack or Bluetooth, and we already have a Sonos Move for listening to music around the house. I don’t know the details on the speakers but they were likely very average quality when installed 11 yrs ago.

My limited understanding of home audio leads me to believe this was a very underpowered way of driving so many speakers. I’m looking for guidance on how best to set up and use the current speakers, without spending too much cash. I would like to stay within the Sonos ecosystem. I have a Sonos arc, era 100s, and Sonos woofer that will be connected to the TV in the living room. I also have one Sonos amp but my guess is I would need several more amps to power 11 speakers, and the amps aren’t cheap. If someone feels strongly that I need to just replace the 11 yr old speakers with something else, please let know. I know Sonos has in-ceiling speakers, but 11 of these would be pricey.

Thanks in advance for any guidance you guys can provide.