Definition of hard-lid ceiling?

I have a situation where I cannot eliminate a sloped acoustic ceiling with a gyp ceiling, and the walls do not go up to the deck (they go to the underside of trusses). To enclose the room, I would like to sheath the underside of the trusses with plywood, taping and sealing all the joints to create the hard-lid ceiling. This would be hidden by the acoustic ceiling below. Does anyone have any idea if this approach would be acceptable, and would it satisfy the definition of a hard-lid ceiling in lieu of using actual gyp? I feel like we are meeting the intent, without sacrificing the acoustics and the asthetics of the room.