I just did this mod on the pleathers for the HE-400. Everything is only taped together and doesn't look nice but atleast I can test them out.
First impression: wow, it really works.
There is no eq-ing going on here, and I hear no tizzy treble, and the the recessed upper mids are completely gone. No need to boost those frequencies with an eq.
Thanks Jerg, you're brilliant!