Custom Multichannel audio... not in surround?

Hello,

My question concerns unity's audio spatialization capacities. Our speaker setup is quad.... but not surround, they are in a straight line. This is for an immersive installation, not a game. We are developing the visuals in unity3D and would like to have sounds following interactors as they walk along a long screen (10 meters). Four speakers are spread along that screen.

The issue is that in unity it seems that all multichannel configurations are bound to surround. Is there a way to "place" speakers where we want?

My first thought was to use multiple audio listener, one per speaker, and attach sound sources to the interactors movement. But multiple audio listener is forbidden.

Thank you very much