If you're going to do multiple sets of speakers per amo, I'd go with the speaker selector/impedance limiter route. It's more clean for your Amp to help regulate the power to a $50 piece of equipment vs frying your $700 Amp.
Your other post is basically exactly what I suggested except for adding the volume controls on walls, which your installer pointed out may be tough.
If you put the amps and those selectors in an accessible spot, you can certainly just control the volume from there (or turn off zones).
Ours are way back in the master closet (by design), so the wall volume controls are key for our setup. If we had them in a cabinet in the living room, it'd be different.