I have heard ZMF are treble shy in comparison to Empys, but never listened to ZMF myself. I compared Empys to Audeze lcd 3f and despite being a bit more bright Empys are definitely more smooth (treble is not piercing). But this is very subjective and one may feel some harshness where others do not. For myself i was surprised by lcd3f that i found them harsh despite being darker than empys.
You can certainly limit harshness with cables and dac. Cardas parsec is a good cable with this respect. R2R DACs as well. I personally have just bought Neko d100 DAC. Not sure if i will keep it, it is still burning in, but it seems it is a harshness killer
Interesting comment about ZMFs being less bold.
@TheMiddleSky is that "bold" difference significant? I guess it is because planar drivers.