I find it funny that there is amazement this isn’t possible in 2019(!) yet using an AVR for multizone audio was all the rage in 2009, and that’s pushing it by 5 or so years IMO.

I agree with the last couple posts, stop using an AVR for anything other than a budget media room. AVR jack of all trades master of none and such.  If the proper solution isn’t in the budget then they surely aren’t going to be willing to pay your service call fees (for phone/text/email and on site) every time they have an issue with the system they talked you into.