A note on soundstage:
Soundstage on RE-400 can be perceived in different ways depending on which tips you use or if you mod it. Personally I don't have a problem with it's soundstage anymore here is why.
I bought the Sennheiser HD-598 first and almost immediately liked its soundstage. A month later I bought the Sennheiser HD-600 and thought its soundstage was boring. With time I realized I prefer the soundstage on HD-600 compared to HD-598 because when listening music with HD-598 soundstage is wide all the time regardless of what song I'm listening to whilst in HD-600 it is wide when the recording calls for it (live music for example). So in this regard I see HD-598 as "fun" and HD-600 as "natural".
That is why I like the RE-400 so much because I find it natural.