One thing that is not discussed here very often is treating the ceiling for first reflections ... I have to have the center channel above the screen and when I ran the first reflections proggy that is available here on the site ... as a result my intention was to treat the ceiling of my theater for first reflections
... I then broadened that into combining it with a star ceiling.
This a long way to suggesting that if you do drywall a ceiling you CAN have access doors and hide them with acoustic treatments
How often will you really need to gain access anyway ? ... moving a acoustic treatment to get to a access door would be rare I am guessing