[iDark]

Hello fi-ers I bought my Westone 3 in 2009. After the purchase I was a happy man since they met my expectations and of course my sonic preferences (hence my inactivity here on the forums).
 
What I liked about them was the V/U-shaped sound with impressive bass emphasis in your face - as some would say. Decent treble, and an overall pleasurable listening experience for me. So 3 years later I'm planning on selling the W3s and upgrading to something similar like the W3, but on "steroids" if you like. I've heard about the W4s and they we're the initial trigger for me to consider a new purchase.
But from what I've heard, the W4s are lacking the bass and sound more balanced, neutral. This being fine by me, but still not my own personal preferences as I've grown to like the U-shaped sound. (Maybe that's a bad thing)...
 
Edit: Also I forgot to mention that I will be using my iPhone (+ unconfirmed amp?) as a source. Stupid I know but I'm using the Spotify application which allows me to have loads of music. 
 
So final gather of thoughts - Is there a universal IEM or custom at a fair price that would be considered and upgrade from the W3s that I have right now. My budget ends at $700 ish
 
I appreciate all help!