No, this isn't easy. In fact, it's incredibly painful to achieve. HDMI has all but made distributed audio a complete nightmare.
Why? Because you can't have two channel stereo at the same time you have surround sound.
You also have a bunch of zones which aren't surround sound, and you are trying to say that they won't even be stereo, but will be 'mono' areas.
Do you want them all to just play the same thing at the same time at the same volume or do you want to have individual control in the different areas to pick and choose what is playing and at what volume it is playing?
This is what distributed audio systems are for. You need to feed analog sources to the distributed audio system. Many cable boxes still have analog audio outputs, and most receivers can feed zone 2 a digital source (HDMI) out of the analog outputs, as long as that is the same source playing in the surround zone at that time. This is great for devices like a Roku or similar which doesn't have any analog audio outputs.
Receivers are meant to play back in a surround zone. Maybe a second zone. But, if you want three or four or more rooms with audio then you need to step up to something designed for that purpose. Just using a surround sound receiver as a multi-room product won't leave you feeling happy.
On the 'easy' side, you can just use a good power amplifier and hook up volume controls in all the rooms and use the volume controls to adjust volume while every room plays the same source.
If you want different things in every room and you want to have individual wall controllers, then you can get something like the Monoprice distributed system...
Distribute and control music and other audio material to up to six stereo speaker zones using this 6‑Zone Home Audio Multizone Controller and Amplifier.This multizone controller is a 6x6 matrix
www.monoprice.com
Going to phone control...
Whole-house audio systems you can install yourself and control with keypads and smart devices. All HTD electronics include a 30-day guarantee, 2-year warranty.
www.htd.com