I find that an ep-630/cx300 is also noticeably weaker than the KSC-75 in SQ. No question, really: the detail resolution is two removes better. Cheap canalphones aren't entry-level hifi, they're acceptable midfi that fill an important gap for cheap portability.
Among in-ears, you have to move up to something like a Vibe to really give the Koss a run for their money in a sound quality contest. I spent an hour recently A/B testing the trusty KSC against my pre-production Vibes, and though resolution was only about the same, in most other ways (like speed, tonal balance, and strangely even soundstage) the Vibe took the laurels, and my KSC-75 moved to a drawer.