Due to some of the tuning solutions implemented in the IE800 I think it may have more variance in the treble region for listeners than most IEMs. I personally found it a little thin and splashy. The K3003 is not exactly a hallmark of smoothness what with the TWFK driver and all, but it's not splashy or tizzy (and you also have the three tuning ports, which affect treble most strongly, to play with). Soundstaging is a close call. I would probably still give the nod to the K3003 because the bass of the IE 800 can be a little more intrusive, which isn't great for soundstaging.
My comment here has a little more info on the subject of the IE 800's treble: http://www.innerfidelity.com/comment/488906#comment-488906
I don't really want to comment on the sound of the Shures as I really hated the fit and it's very possible I didn't hear them at their best. Don't want to steer anyone away from what could potentially be a good earphone for them. It just wasn't for me.
did not know about that comment... what i still don't know, is if ie800 has more treble? my actual rig has.. let's say that the treble is louder than the rest of the music. and i love it. this is why i am debating between ie800 and k3003. i want as much treble as possible, even more the very high end of treble 12-20khz.