For what it's worth, the CM5 is excellent. Back to back with the ES3 it's very difficult to say one is outright better. The UiiSii sounds more natural than the ES3 but no less detailed. The ES3 has more "air and sparkle" to the treble (characteristic of a balanced armature) while the CM5 is a tad laid back. Bass impact and tightness is very similar on both. The packaging for the CM5 is miles and miles nicer than anything I've seen from KZ and the earphones themselves feel slightly more premium due to a nicer (but non-removable) cable and a frosted inner shell. At their respective price points, it's a toss up and you could easily justify owning both.
Perhaps more pertinent to the discussion, both the ES3 and the CM5 are IMO in a class above the dark and fuzzy sounding ZS3 (which are plenty fun, but simply not competitive on detail retrieval).
I'm a basshead but i still didn't find a pair of headphones that can bring me much bass (that is fast and has good extension) and sub bass even giving me clear mids and highs.
Every headphone i tried has a recessed part of the spectrum, like the mids in the case of zs3 and memt x5.
I seriously can't understand where should i look for even if i guess a headphone like the one i just described and the one i'm wondering doesn't even exist, or if does, it costs so much money.
Many people anyway told me good things about es3 but i even heard it's very bright and might not be liked by bassheads.