The two connections are probably more useful for bi-wiring (one amp, two sets of wires) than bi-amping (two amps, ideally with electronic crossover before the amps), since both sets of terminals still go through the appropriate portions of the crossover.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8