Unfortunately not... Sibilance (and treble in general) problems with HE-400 are very well-known. I personally found their bass too dominant but I can understand many will find it just about perfect. Still, there is no way you could call the bass of HE-400 weak or hidden. Well, you could... But I have never seen anyone calling HE-400 bass shy honestly.
I am not sure you really disagree with me. The sibilance / treble characteristics are not what I really call "problems". I've heard many, many speakers, and they've been far more out of balance than anything I've heard out of the HE-400s.
As for bass, I myself preferred a 3 db boost @ 50 hz. Needed the extra weight. Lol. The HE-400s are not neutral, but they are much more neutral than 90% of the other stuff I've heard.