why not look at 5 drivers in this configuration.....

Which configuration?

5 IPAL21 would make 12.5KW, which is good, because you always want to have a little in reserve.

one top one bottom one on each side and one on the back ....... mount the top/bottom and sides at 33 degrees ish.... to each other and the back one square to all 4......

Yes, I see. That makes good use of the space in order to fit all the drivers in. So that settles the K10S design for now, we can worry about details later.

Lets move on to the K10T 10,000 watt tops box. We could aim for 4 bands:

Upper bass 5-7KW
Low mid 2-3KW
High mid 1KW
High 1KW

I am making the high band 1KW rather than 500W so there is power to compensate for air absorbtion at very long throws. K10 speakers should be compatible with long listening distances eg 800metres

ill get my thinking cap on..... this could be the tricky bit.....