The other issue I see is tonality. It is pretty easy to tell my LCD-5 and 6XX apart just based off of their tuning. You could try EQing both to some target to try to minimize which would be interesting with the other blind folded stuff. Just would have to make sure all headphones could take the EQ because a 6XX just can’t handle sub bass as well so definitely a roll off like the 6XX has naturally.