Plywood Ceiling Solution Found!
I've called some manufacturers and an architect and received 2 different and tested solutions so far:
1 - Rondo Furring Channels fixed directly to the underside of the i-beams and then the plywood panels screwed to the channels. (Architect's solution.)
2 - Use the Rondo suspended ceiling system and suspend it from the purlins. (I thought this could only be used with plasterboard but Austral Ply told me it's commonly used with plywood as well.)
That answers my question. Now to make it happen.