... sound batting and/or weighting speakers ...

Hello to all... 

Need some thoughts and/or suggestions: I am using a pair of KEF Q1s - luv the sound, so much more full than I ever expected - and the driver has such cone extension that the speaker box really vibrates. Now - I am assuming that the vibration really = the possibility of distortion ( or a smearing at higher volumes, tonal deformity, if that is different) and I am wondering if this is more controllable by:
Adding more sound batting into the enclosure (thru the bass port)
Weighting the speakers with a bag of lead shot (?) over the top of the driver/cabinet box ( the cabinet is not flat on top, so I can't use a brick or solid weight; I'm guessing the weight should be something moldable, so the lead shot in a bag is possible if I can figure a way to affix it to the cabinet...)

Thoughts? Suggestions? Alternates?