Wayne,
In the picture provided is that the 2pi tower without the baffle?
If so you have 3 sets of braces but I would swear the plans say I would use 2 braces. 1 set under the woofer and the other set 15" up from the bottom. Did you just maybe make a place for the insulation to sit up at the top of the cab and maybe it isnt a brace?
You also say the braces should be slightly preloaded. Does this mean that you would build the cab as shown without the baffle and the braces cut ever so slightly bigger so they have to be somewhat forced into the cab creating a tight fit?