I don't know how you would get the audio from the projector on your wifi network. Apple Express and Chromecast are receivers and only have audio outputs not inputs.
You could connect any wireless audio transmitter to the audio output of the projector or to an HDMI input selector with audio extraction, The matching transmitter would feed an input on whatever you would be using for sound. Could be bluetooth but there are other. Low latency is important since you might get a audio delay.
Make sure that the HDMI input of the projector sends audio from the analog audio out of the projector. Some don't.