When there is interference between subsystems, you can't EQ that out. When two drivers cancel, the more energy you throw at them, the more there is to cancel. So if a crossover isn't setup properly, no amount if EQ can help.If there is resonant peaking, that can be reduced by EQ. If there is rolled off response because of mechanical mass or inductance, that can be EQ'ed. But if there are ripples in the crossover region, that's not something you can equalize away.