[someweirdperson]

All the x.y multi-speaker configurations are missing a "top" speaker. Why hasn't anyone invented that yet?

For the recording, with the ground transmitter stationary, it could be separated by one receiver shilded to look at only the ground transmitter, and a second omni-directional one for anything flying.

[etskinner]

The human ear doesn't really have the ability to determine the height of a source reliably, only left/right. A better effect might be putting the audio out of phase on left/right, which usually has the effect of making it difficult to hear where the sound is coming from (it kind of makes it sound like it's omnidirectional like you mentioned)