The two (L/R) channels should be exactly the same.
IMO - It would be more useful to compare ^that approach^ to just bridging the amp. Which was the counterpoint I made earlier. I think it is worth trying both your Bridged-mono idea, as well as the upper/lower stereo.
To really get more advantage from bi-amping it could be useful to have the bass frequencies removed from the MR/Tweeter channel. Then that high freq channel has a lot more voltage headroom. However that requires some active filtering to happen between the preamp and the power amp.
Any analogue approach will alter phase, and the only digital approaches that would not alter phase are FIR based using symmetric filters. But that sort of goes somewhat orthogonal to the 6dB/octave crossovers in a Vandy.
Using a Vandy sub requires the Vandy crossover, which also is scraping off the bottom content which has the high voltage excursion. Conceptually it is similar to what we are discussing… and probably a better and more easily heard improvement over using two amps to power the speakers??
Or maybe both (sub and 2x amps) are most optimal.
