Well I've always assumed that time alignment can be achieved regardless of crossover type (1st,2nd,third order) and regardless of HF, LF wired in same polarity or reversed polarity.
It seems that time alignment is achieved most easily by physically positioning HF driver with respect to LF driver. (A7)
Why not then connect the HF and LF drivers in the same polarity and adjust time alignment by positioning the HF driver. Theoretically then when the signal begins the cones and diaphragms begin moving in the same direction. And even though a 2nd order crossover introduces a delay, can't it be compensated for by physically moving the HF driver? (phase alignment)
Probably missing something here so feel free to enlighten me.
(I'll have to go to biamp and active next)