UM3X - no, specific emphasis to bass and treble
CK100 - yes
SE535/SE530 - yes
DBA-02 - no, mostly emphasized treble, lean even in the lower mids
Custom 3 - maybe, not bad actually but mids are not its key feature, well balanced though, outstanding bang for the buck
E-Q7 - unsure (haven't heard, but a yes from reviews I've read)
FX700 - unsure (haven't heard)
SA6 - yes
SA7 - unsure (here's to hoping)
MTPC - unsure (only heard the Gold, maybe given the Copper is more detailed, Golds actually had excellent midrange presence, muddy, but well presented)
CK100 - very pricey but excellent throughout
SE530 - excellent buy if mids are all you care about, cheap that they now have a successor
SE535 - worth the huge price difference? Maybe not if mids are the only goal
E-Q7 - haven't heard but mids are a big focus of these and are apparently quite good from reviews I've seen, a bit pricey for a single BA driver IEM
SA6 - a completely overlooked earphone, outstanding mids, transparency, air, natural note, compact, light, and isolates well, you may be better off waiting for the SA6R though
MTPC - maybe, can't comment personally, was surprised by how well the midrange was presented with the MTPG, well balanced, but it was a thicker, sluggish presentation, Copper's supposed to be a bit different, quicker in note
ER4S - why not another pair? It's an excellent product, stay with it if you don't want to change anything. If you do want a change, how do you want it to be different?