Speaking strictly for myself, my take on the Empyreans, which I use with my A&K Kann Alpha, is that they excel in many areas, in fact, most areas.
I would say that, for the bass area, that it is merely not the Empyrean's strength, but it is more than adequate.
Put it another way, one would not likely say that the Empyrean's bass is their #1 attribute, and the raison d'etre for buying them.
Yet, the 30 Hz to 120 Hz region is not a weakness (for me). It is merely not their best strength.
Taken as a whole, the Empyreans do so many things so well, that I consider them to be an outstanding, non-fatiguing, highly musical, enjoyable, comfortable pair of headphones. Well done!