I'm not sure if these just passed some burn-in threshold or running them through the impedance adapter for a long time did something but I listened to them today unamped & without the resistor adapter and WOW.. it's like they were reborn or something.. just gorgeous balance.
The midbass hump has now completely smoothed out and the bass has become really well textured and much better controlled. Out of the box, the mids were a bit dry (for my taste) and recessed.. not any more.. they have just the right level of lush and thickness without muddying up instrument separation. The mids have moved forward to come into excellent balance with the deep bass and shimmering treble. They're simply in perfect harmony with the bass and treble now, where they were a little recessed before. Vocals, snares, saxes, delicate percussion, and everything else that plays in the midrange sound really good and much more clear now.
The treble clarity is now better than it's ever been to my ears.. I'm amazed a budget dynamic can turn out this kind of ridiculously crisp, clean, treble with excellent timbre & no sibilance. It was a little hot out of the box but their potential was evident.. now the rough edges has smoothed out and the treble has fantastic definition.
So, no more need for the impedance adapter with these now.. unamped, they're an absolute diamond in the rough. Color me IMPRESSED.