"Attempts at increasing the top end of the 12 were unsuccessful, and as such the boxes exibit some harshness around 2kHz thanks to the 2" HF drivers"

I take it that ideally, you'd want to cross the two driver above the the 2.5KHz range, but the Kappa's couldn't be extended that high. That in your speakers, the 2" compressions are taking care of business at 2kHz and is the cause of the harshness.

Is this correct?

thanks,
gcl.