My first in-earphone is ER6i, but i started to like X10 once tried in HIFI show. This is because it is so comfort and balance for all frequencies.
But don't expect the 立體感 as good as those twin/tri-drivers earphones and this thing takes time to run in.
However I think UM1 is not bad ones even thou the sound not too good because it is only 2 days old. At least can give you some details which ER6i may not be able to express.