iTunes is very accessible (as is most of the Mac) by AppleScript. So sending iTunes (or other Mac audio) to AirPlay devices is pretty simple, except for one thing…
Latency - Airplay has lots of it. This is one thing that makes Sonos “worth the money”; they work very hard to eliminate it. You can pipe music to multiple devices throughout your home and have pretty much everything in sync as you move from room to room. This rarely happens with AirPlay, but if you’re only concerned with one room at a time (or don’t care multiple rooms aren’t in perfect sync) you’re golden.
I have an app that when I am “away” and an outdoor motion sensor triggers (or when the doorbell is rung), fires up my main audio system and plays two large angry dogs barking. It loops through several of them (plays one, next time selects another, randomly), and is pretty realistic.