Crown install was successful with a quite a bit of wood left to spare.
Here are my two helpers looking all angelic like. They really helped me with hanging 170" inches of crown on both long sides of soffit as well as the short sides.
I first assembled my two scarf joints on my work bench with a thin strip of 3/4 inch plywood and a couple pocket screws.
I figured if I connected the joints off the wall it would be able to hide them well and get the tightest fit. That was a correct assertion. One of the joints I had problems with and is visible but the other is barely visible.. take a look:
Here is the overall look.. the theater is a bit more warm feeling now..
I did goof on the rear right corner... somehow I managed to cut the crown 1/4 inch too short. I was able to hide it well but not before accidentally ripping down the rear crown and backer in the process.
I was able to get the backer back up nice and tight and then position the crown to hide the 1/2 inch gap. You cant really see this mistake unless you stand underneath it and look up at the 1/2" gap between the crown and the wall. I guess I can caulk it, putty it, or stuff wood in it so that light doesn't show through.
I also goofed on the little 90 degree crown stops that meet at the projector. I realized after breaking 4 or 5 of those little crowns that they were too thin for brads. I eventually ended up gluing the left one on for a perfect fit, and the right one I was able to nail in the right locations but with a slight gap in the upper corner. I did notice it is halfway cracked but not visible so I might just leave it alone until it breaks then cut another and glue that one on as well.