Problem solved, and I'm happy now.
Well, finally I learned it the hard way by making mistakes today.
As you guys pointed out, the problem was the wrong speaker connections on the back, not wrong hook-up between crossover and the amps.
4343 has two sets of binding posts on the back cabinet: the lower posts for LOW (300Hz), the upper for HIGH, when you bi-amp.
But upon closer look, I found the cables connected wrongly between the posts and the amp inputs.
Looks like I mixed them while I tried different speaker cables recently.
As a result, however correct the cable connection between crossover and the amps,
I heard this strange reversal of LOW and HIGH sound.
Anyway, thanks so much for your waking me up to the importance of correct wiring once again!