Thanks for the reply! I did make sure to check the drivers after getting the headphones (using your diagram, appreciate that) and there were no apparent issues. I also used
this test to check for imbalances and nothing too glaring aside from some rattling on the bass shaker with the small amp.
As for previous headphones, I was using an older pair of hyperx cloud 2s which served great for 5+ years. With EQ I certainly like the HE6se more, although I am having a hard time recognizing the difference between open- and closed-back (namely the lack of an expected soundstage).
Is it possible that not using a proper DAC/preamp is limiting the FA-10? I was luckily able to pick mine up off the used market so if I decide the difference is negligible it should be easy enough to resell. I may plan to keep the headphones either way as I do enjoy how they sound at the moment, but would like to make sure I'm getting everything out of them first.