I've been using the UE400's the most expensive dynamic driver IEM from UE for the past 5 months. I like its clarity and detailed sound, sparkling treble, and a wonderfully spacious sound-stage. Only thing I don't like about it is the Bass, the bass is noticeable but it seems to just miss the mark, frankly the Sennheiser MX470 and 581's in my opinion punch out better bass.
The Bass on the 400s feels like a hadouken that just disappears just out in front of you, its not impacting but it's noticeably JUST there.
First thing though I am not a bass head, but most of the music I listen to often has Bass in it to compliment the song (Jpop etc). So I don't like overwhelming thumping beats but enough for a complimentary partnership with the music.
But Anyway on to my main point, I decided to one day switch out the stock tips for some Sony tips (some spare ones that came with my EX300). Plugged the UE's into my Walkman and immediately the Bass was more noticeable than ever before, I can feel it all the way down to the sub-bass level and it is vibrating!!!!
The bass was more noticeable, still controlled and did not feel bloated or bled into other areas of the music. Combine that with the already excellent properties of its clarity, detail, treble and soundstage, I am very proud I made the switch and have been using these quite frequently.
I did the same to the single BA UE600's, the Bass was still enhanced a little but the difference was not as noticeable. Perhaps it is naturally due to Balanced Armature vs Dynamic.
Just my 2 cents!
Maybe you could benefit from this UE400+Sony tips combo!