However, my chromecast audio stopped working (possibly related to the product sun-setting?), and I was surprised to learn that Apple no longer manufactures the AirPorts. What kind of audio receiver did you use? I ended up purchasing a "new" AirPort Express on Ebay, but how else does one use AirPlay these days with off the shelf audio equipment? I couldn't find anything helpful via googling.
It has an RCA output for “Zone 2” which goes to the whole-house 8 channel amp.
I already had the receiver in my living room for my 7.1 audio setup for watching shows/movies. So it didn’t cost anything to hook up the Zone 2 other than a $10 cable.
I vouched for Cecja’s comment below. If you don’t have a WiFi device which can output analog audio and receive AirPlay, you can actually rig something up using a Raspberry Pi and open source software. Since there’s nothing to configure ever after the initial setup your family shouldn’t have any issues using it - it should “just work”.
If you want to be able to play different streams to different rooms, I think you could even do it with several RPi’s each as their own AirPlay target, and then each wired to different channels of the amp.