Regarding performance, I can only state that my personal gear used that I mentioned before (JBL SR4719X's and SR4733X's) is ok but of course does not have the coverage (loud in front and drops off after about 30 feet) in a school commons environment. I am certain that we exceed 100dB at about 40 feet easily but no one complains! The new room is slated to contain about 300-350 seats. All funding now is designated to the facility and $0 for sound reinforcement. A future capital drive will fund the main system later. The ceiling area will be addressed to support a LCR hang unless there is a system that can provide the proper coverage with just LR. I am sure that we can use donated funds for the subs as soon as a decision is reached.
Well if yo uput the subs under the stage, you are going to have exactly the same problem you have now. Loud in front and quieter in the rear. NO way around that. No mater what speakers you choose.
If you want more even coverage, then you will have to fly the subs-and now the conversation takes on a whole new set of parameters.
Changing the subject, if you look at a LR situation, then you have to consider what will happen right down the middle of the room. Unless you do panning on every instrument or are seated directly in the middle of the LR, you will all kinds of interference. OF course once you start to pan various channels, it will sound different on each side of the room.
For a low budget situation, you are MUCH better off to start with a center cluster and have fills as needs to the sides (NOT as a left /right speaker) but as fills pointed down and out from the main cluster.
Since you have no budget, you need to determine what is most important to you-loud or low? I would argue that in most cases if you have subs that are actually flat to 40Hz (not 10db down-flat) you will be Ok. If somebody wants deeper bass-ask them to pay for it.
I know it seems like petty things, but the arguments about stage height are VERY relivant. It sounds like you are being told very different things regarding the ACTUAL AVAILABLE HEIGHT for a large speaker cabinet.
I can say without a doubt that the person who told you 19" on a 21" stage is completely wrong-there is no way you could put a cabinet under there-without the stage either falling or sagging when somebody walks on it. The span is simply to long. They were not taking into account the joists (which is what Brad and I have been trying to point out).
Those are VERY real and VERY much in the way and HAVE to be accounted for.