I've been using mine a lot lately with the Magni, but I still can't figure out why mine only sound goods with the filter foam removed.
People said it has NO effect on the sound, but for me it definitely does. When I install any foam it chops off the treble and makes it more muffled sounding.
It's not subtle at all. I even tried pillow stuffing, but it sounded as bad as with the filter foam.
Maybe there really is a difference in sound between the stock AKG foam and aquarium filter foam? I don't think i'll ever figure this out...
The soundstage definitely got larger with the Magni and it seems to make it sound clearer. My Sextett seemed to not have a whole lot of treble, but without the foam it's OK.