Airport Express Stopped Playing iTunes on eero wifi network

I've been using three Airport Express with iTunes devices for years on an eero wifi network to play Music from my iMac to three different stereos. One is a 1st generation Airport, the other two are 2nd generation. All three suddenly stopped working with Music a week or two ago. All three Airports are set up to join the eero network. In Music on my late 2012 iMac, I can see the Airports. I can click to turn on each Airport. But soon after, the check mark turns to a dash, and music won't play to the stereos connected to each of the Airports. Sometimes I can turn off wifi at the iMac, quit Music, turn wifi back on, and restart Music, and it might play. That's not working at the moment. Yesterday I reset one of the Airports to factory settings and completely reconfigured it to join the eero wifi network. After that, I could play Music through all three of the Airports to all three stereos. I let Music play for nearly 16 hours, and it never failed. Then I had a power failure this afternoon. After restarting everything, once again Music won't play through the Airports. I'm at a loss. I spent nearly two hours on the phone with eero yesterday and got nowhere. They had me restarting lots of things, making sure the eero software was up to date, and lots of other stuff. Eero regularly updates the software for their routers, and I suspect that their March 2 update is what caused this incompatibility. Eero finally threw up their arms and said call Apple, but I know that Apple will tell me (1) my computer is too old, so I must buy a new one, and (2) they no longer support Airport Express. My system was working just fine for years, and then suddenly all three Airports stopped at the same time. I'd be most grateful for any advice.