Not quite done but I thought I'd share where I'm at. My objective was to have a simple way to play background music in the house from our Apple devices. Cheap.
All the network, video and telephone wiring comes back to the same unfinished corner of the basement so I routed the in-wall and in-ceiling speakers there too. This is my workshop and I wanted the components up and out of the way. Originally, I'd thought to build shelves or hang a normal cabinet but I realized that I'd need access to the back whenever anything changed. So I hung the cabinet on drawer slides so it can be pulled out from the wall when necessary. The side rails are spaced to hang standard 19-inch rack mount stuff.
For WHA, I'm using speakers and wiring from Monoprice. The amp is a DaytonAudio MA1240a purchased from PartsExpress. I currently have 4 Apple Airport Express units (Model A1392) connected to the amp. One for each current audio zone. I picked them up used for a few dollars each (CAD $35-50 each). They provide the Airplay2 input to the amp. Note that I've disabled their WIFI networking functions and they are hardwired to network switch (immediately below in the cabinet).
From an iPhone, iPad or Mac, we simply pick which zone or group of zones to play to:
I'm pretty happy with the results. Sound quality is quite acceptable to my old, abused ears. Almost any source on an iOS device plays through Airplay2.
I plan to change the network switch wiring and turn that unit so the connections are at the front rather than the back. The patch cables need to be a foot longer to do that.
If I had this to do again, I'd try to do a better job of cable management. There is a metric tonne of network cables, speaker cables, and line-level audio cables. There are 10 powered devices in the cabinet at present. The WHA stuff is surge protected. The network stuff is powered through an Uninterruptible Power Supply so it doesn't go down when the power blinks. Two power bars are mounted to the bottom of the cabinet to supply the juice.
An annoyance is that the amp takes about 8 seconds to wake from sleep. Compared to a table-top radio that comes on instantly, that seems like forever sometimes. I'm considering setting the amp to never sleep. Not sure how much electricity it would use if idle but not sleeping. Also, it might be possible to use Homekit to automatically wake the system each morning...which is when I find the lag most annoying.
I plan to add a pair of outdoor speakers to our patio if the weather ever improves. Also considering adding a pair to my workshop.