I also have both the K10 and the SE846. While the SE846 is definitely an amazing headphone (I think there is definitely some magic involved to get a 4 driver IEM to sound that good), the K10 is just a technically superior headphone.
To my ears, the SE846 has just a bit more amplified feeling on the lows. It is like somebody turned up the amp on the bass guitar and kick drum while leaving everything else alone. This is with the balanced filter; the black filter is even warmer, and the white filter is just a little too silibant for my tastes. I think the balanced blue filter suits my tastes the best.
The K10s are more neutral. It doesn't feel like somebody messed with any part of the frequency. Everything is where it should be, and the levels across all frequencies are just about perfect to my ears. However, if a piece of music calls for a big bass slam, the K10 can definitely deliver in spades. Additionally, the K10 is never sibilant, which is awesome if you are as sensitive to that as I am.
I think that what you get with the K10 is just a bit more refinement in the playback. The bass isn't as present when it isn't called for, but if it is there you'll have both more quantity and a bit more controlled quality in the K10. The same is true across the spectrum: the mids are just a little bit more clean, and the higher treble just sparkles a bit more. Listening to the decaying ringing of a cymbal hit just sounds more true to life on the K10.
I think the biggest thing that a K10 will get you is better layering, better imaging, and a bigger sound stage. The SE846 is by no means a slouch; I would probably say it is about 90% or slightly more of the overall quality of the K10. However, if you really want the best possible playback experience that money can buy in an IEM, and you want that slightly larger bass slam or that last little bit of sparkle, you will definitely not go wrong getting the K10.