The driver's Fs is an octave higher (200Hz), and there's a natural rolloff already at 30dB@100Hz, so that will be pointless. I think people are having a problem because they are trying to get some midbass out of these puppies and it just doesn't have the displacement potential to do so. For use as headphones, this may be feasible, but not for normal audio use.
Granted, a filter is always a good idea, but if you can tune via the enclosure to meet the application, there may be no need for one. The less degradation and signal loss, the better.