Momentum On-Ear mods:
-Dynamat Xtreme dampens driver and main chamber vibration, resulting in tighter bass without boom and the mild bloat that it has stock. The upper mids and lower treble no longer have as much edge as before, they're mellowed out a bit which they needed in my opinion. The bass will not thump as hard as before, either, but the sound still remains very bassy.
-Two 4mm thick pieces of open-cell acoustic foam (I have Akasa Paxmate Plus) to soak up some of the reverb in the secondary chamber. The reverb in the secondary chamber masks the lower midrange a lot, and the bass as well to a lesser extent. With reverb reduced, some soundstage depth is lost in exchange for clearer, cleaner, more refined lower mids that better match the upper midrange and the bass is clearer and cleaner than before. Now the midrange is much more balanced and the lower midrange sounds about as good as the upper mids.
I like this headphone far more, now. There is a little delicacy to the vocals now that wasn't there before, I think. Maybe I forgot after not having used the headphone in a while.