Rollk2
500+ Head-Fier
I wouldn't consider any of these an upgrade to the FA-4, honestly. I haven't personally heard the SE846 or Rox, but ears I trust have told me that they don't live up to the ears.
I agree, but with nuance. The Rox and the 846 are not profiled for the same use and they don't share characteristics. In fact they are little more detailed than the FA4, but not far, but have more body and more note weight. Rox are significantly larger at the bottom of the stage but both have a great deepness. The 846 have a lot of more note weight and have more speed but both are close in terms of soundstage unless the FA4 project further and the 846 have more height. The 1+2 is less coherent and neutral but have an enormous and unrealistic soundstage that projects far. Both are open sounding but differently. The 1+2 have more height, is wider, but both shares capacities in deepness.
To my mind the only upgrade in that category is the custom, all other universals have sometimes more details, sometimes more musicality, sometimes more headroom... But no one is able to cumulate all of theses qualities. And it's pretty hard to find that kind of exigences among the custom IEMs.
Hum, and The 334 are not dark neither bright but they have plenty of bass that are not extend but sound loud.