If you mean you want to use the wired speakers along with 2 AirPlay speakers at the same time, the delay would drive you crazy. Without using a computer or an iphone to AirPlay to your speakers it shouldn't work. The whole point of AirPlay is to stream from your apple device to a receiver, Apple TV, another device... Do a few searches for AirPlay transmitter and you find a lot of Chinese apple knock offs. I have everything apple but I'd still wire it if I were you. Grab some 12v low voltage buriable wire from Home Depot. Grab a flat end shovel and bury it 2" down and call it a day. Just put the shovel down 3", rock it back and forth and shove it in ther. Step on it to close the seam and your done. There's no power it's just speaker wire. It'll take an hour. You could also cover it with mulch or rocks.
The setup looks awesome by the way.
If your buying a new projector, buy more lumens than you will use. Running it in "Eco Mode" makes your bulb last 20-40% longer and reduces noise and heat.