Well either way, the actual sound
would have to be produced by something else that accepts Midi. For what you want to do, a computer would be easiest, not 100% sure, but I don't think a "16 Speaker Midi controlled sound module" Exists.
As far as how to do it,
I'd probably define each speaker, then the code would look like,
xPot <50 >100 & yPot <50 >100
speaker1 = HIGH
midi.send(speaker1, 2, 3)
And so on, this would be pretty "monotone" where the sound would jump around, unless you define halves, but that gets really complex.
There's probably a way to create a more efficient table of some sort, but that's the best I see.