I know I’m going to go against everything the forum stands for with this answer but honestly in this instance I would advise you are better getting active PA speakers (or maybe large studio monitors) than building your own.
If I were to fill a room that size using my normal choice of d&b audiotechnik PA speakers Id be using 2×8″/1×1.4″ cabinets capable of 400w rms and 132db@1m with amplifiers capable of 1600w rms.
It is very surprising how quickly sound pressure can drop off as distances get bigger and I’d be very concerned with smaller speakers/amps keeping up with the range dynmaics theatre and film contains at sufficient SPL to fill that size room
Of toids speakers the soundstage 15 is the only one I would be willing to recomend for this use case but you would need bigger amplifiers than the one you are currently looking at e.g. multiple PA amps not a HT multichannel amp.
The problem with this is the cost.
For example for the same price as 7x soundstage 15 and 1x AD3700 you could get 7x active PA speakers of approx $550 per speaker. You can often find 700w 10″ 2 way active yamaha PA speakers for $399. The same idea applies to subs as most active PA brands provide matching subs for most of their speakers
Pretty much every country has some sort of PA/music technology store where you can source these types of speakers more locally than getting DIY parts from USA, many allow you to listen and compare before you buy to make sure they are correct for your purpose
Another big reason to consider PA speakers over DIY is manufacturer support and warrenty. These are not an issue when picking speakers for personal use in your own home but for a public venue this should also get some consideration from you.
The processor however looks fine for the job and can still be used as you intend if you swap to active PA speakers
I know this is not the answer you came here looking for but I honestly think it is the best solution for your community at this time.
