I don't think the issue is HE400s' treble not sounding like HE500's, but that the newer revision (yellow drivers) HE400s have more piercing treble than older (white drivers) HE400s.
Anyway thanks for the reply toward our issue, but could you specify what you guys might do? Make another driver revision? Engineer some sort of precise damping material without changing the revision? Or something else different?
We do not plan to do any change to the latest HE400 because we already made a little adjustment for it (even if it is not perfect yet). Next, we gonna make more headphones which will sound much better than HE400.
You all can take my words here, and we will do our best to accomplish what we promised before. Unfortunately, we cannot tell you what exactly we gonna do with our any stuffs just because it is a SECRET! So sorry, buddy. Other than that, we are so glad to help you out on everything if we are able to. Besides, I can guarrantee everything you get from us will be worth of the money you take out of your pocket.