It might be easier if you put the styrofoam on the floor, then put the speaker on them, then the other styrofoam, then the box over the whole think. Once the box is covering the mass, push and flip the box upright. This way you are not lifting the speakers and putting them in the box which could throw your back, and I kow how that feels. Also this method is a lot easier if it doesn't quite fit because then you are lifting the empty box up, adjusting the speaker and foam until it fits instead of lifting the speaker and foam out of the box until it fits.