Would this room work?

yep.....

What about removing the drywall from the ceiling joists, filling with sound absorptive insulation, and then using acoustic cloth across that. Seems to me that you are very limited in height dimension, so it would be better to build your treatment into your ceiling rather than onto your ceiling.

Great idea Peter. If the walls are 6 feet high instead of 4, that would be a huge plus!

Well, I went back a re-measured:length is 17' 11", width is 13'7", side knee walls are 44" high then slope to a 4 foot wide flat mid line ceiling that is 8' high and runs parallel to the 17' 11'' walls. Room is carpeted over trusses. Walls are 2X6 and listed as insulated and sound proofed and floor is trusses listed as sound proofed.

My tweeter height is 43 inches and the speakers would likely be at least two feet from side walls (where ceiling height is about 5 to 5 1/2 feet) and speakers would be about 5 feet out from front wall

Whatever the wall dimensions and room dimensios are, you can make it work.