What might be done is to first determine that the EQ software is doing what it's supposed to. Electri-Q for instance gives you more or less what you ask of it, whereas the default EQ in foobar does not do at all as you might think it is. Second, to make sure there's a definite aim to the EQing. You need to know exactly how many dB to put into which Hz. This ultimately means to look at graphs, preferably ones measured of the very same pairs you're dealing with. For best accuracy, measuring the two phones followed with convolving the difference would most likely give the exact same sound on both phones - except for soundstage - given that the differences were small to begin with.
If there's no access to measurements, very careful listening will need to be done by ear to establish by how much the two phones differ in sound along the spectrum. Then EQ.