I know what you mean about boomy bass on IEMs, but these are different. They are the dark horse of IEMs imo, not so well known because they are only sold by Sony in Japan I believe, but have sound similar to custom IEMs. Mids are never overshadowed by the bass, despite the bass being elevated. Treble is a little sparkly. It's just a really fun and addictive sound signature.
Anyway I don't want to go off topic too much, anybody know headphone similar to the HE-400i but with more bass?
Why don't you just sell your HE-400i and keep the Sonys if you are so happy with them? And it seems that you are.
Personally I have hard times understanding why anyone would think 400i is lacking in bass and being a disappointing.headphone.