We will have to disagree here. Take what you said about the hd700 vs the he400 and reverse it. I wonder if you didn't type that backwards by mistake. The bass on the he400 is the crown jewel of that hp and to my ears is several leagues above the the he700. I found the hd700 harsh, strident and overall unpleasant to listen to. And yes I listened to it on some very good amps.
The he400 bass is some of the best audiophile quality bass in the game and at $300 you won't even get close with anything else.
What amp did you listen to the HD 700 on? They tend to be polarizing around here, but I also think they are pretty source/amp dependent. Maybe on a brighter amp like the Magni it could sound somewhat harsh. But after 50 some hours of use now, even on the BH Crack (which I find tames the HD 700 a bit too much) is clearly more enjoyable to my ears than the HE-400 including the bass. I find its a perfect balance of detail and musicality. Electronic music especially. My opinion, of course. HE-400 is a fine headphone for the money even with it's sometimes wonky treble. I was only sharing my observations. The HE-400i may change my mind.