I will try to "shift the tweeter crossover down a smidge" with JBL 2123J in place. I need to go back to do some reading for this.
I checked the polarity according to the schematics and "reversed" polarity marks of the JBL drivers in use. Everything appears correct in that aspect.
On another note, I really enjoy my current set up with the TPA3116 digital amp. I used to use a 300B tube amp. I notice one interesting difference: with the tube amp. when the volume is low, the details and expression of the sound seem subdued, but with the digital amp, they are still there, making low volume listening much more enjoyalable.