Your heart's in the right place but that ceiling needs to be opened up like a can of tuna. Each 2x10 needs to be doubled up (sistered) and through bolted with 5/8" all thread ... construction adhesive would probably be good ... screwed, glued and tattooed . The vent hole needs to be in the middle of the 10 inches and away from that notch.
It might seem like a big deal now but it will be a bigger deal later.
Ahmed, nice theater BTW and thanks for posting the pic's. Good luck.