I wasn't forgetting the source, I was assuming the source would be connected to the AVR, then the cable to the projector. Yes, if you are feeding the projector directly from the source then there has to be another cable somewhere. Doesn't matter if it's something returning from the projector, a second cable (most likely optical) from the source to the AVR, or add even more cables if you use an HDMI splitter between the source and the projector to pull the audio out. And since we are discussing a Stick, there is no way to get audio from it except via HDMI. So there has to be a splitter or AVR in there somewhere.
Nvidia Shield, Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.