I'm in love with the transparent, airy, and natural sound of the RE-400s, so I am naturally eager to up the ante and get something high-end that can give me the same euphoric lift from the way these present the vocals. I own the Sennheiser IE800s and not even those do it the same way for me! There is just something about the RE-400s that sounds so natural, quick, and dynamic that keeps me coming back (Seriously, when has a snare ever sounded so snappy?).
P.S. I am aware of the RE-600 and I already own the HE-400 and HE-500, so please give suggestions for non-hifiman products!