If I understand correctly, you have a huge surface a few inches above another surface. You want to put sound absorption between them and supply a huge amount of sabines to the room. However if sound can't get to the absorber then the absorber doesn't absorb any sound. You can add acoustic panels around the perimeter of the platform, say 12" wide and 2" thick. This will provide all the absorption you can get out of this system.
If you can drill an infinity of holes in the platform say 1/4" every inch pattern, then the platform becomes acoustically transparent for all bass and mids up t0o maybe 600 Hz, ane it becomes reflective above this. This is approximated. Then add the sound panel under the floor, remember to leave at least 1/4" air space between the back side of the plywood floor and the front face of the sound panel. Otherwise you will chole the air movement in the hole.
You can use carpet over top of this but make sure you can put the backing of the carpet to your lips and blow through it. You want acoustically transparent carpet.
In highly reverberant spaces the speaker choice is a "distributed sound system". Lots of small low power speakers, probably 8' apart and 10' off the floor.
What is the volume of the church? What are its dimensions? Why such a huge platform? How do you know how many sabines you need? And don't forget the bandwidth of your absorption. If you absorb all highs then you will have a boomy, dead space, for example. Usually there is a curve, that has longer reverb in bass and top end and less reverb in the middle range, 250 through 2k octaves.
What type of service to you have? Is there a praise band on the platform?, no choir so just lead singer?
Churches are complicated, you want low RT60 so the minister can be understood, but then the room is so dry the congregation can't sing and the music minister is not happy or visa versa. I have written many article on church acoustics, reverberant yet intelligible. It's not an RT60 fix. google acoustic sciences, go to church and then to articles. Read. ART Noxon