The audiophile world is one of incredibly quickly diminishing returns, especially when you're talking about IEMs. Those KZ's that you have are a great value and that scales about linearly up to the $100 mark, after that I'd say things begin to drop off quite quickly.
As for why you'd buy CIEMs, its mostly about better isolation and comfort. Your average customs will have a quality on par with universals a bit below their price but will be more ergonomic and isolating. The benefits are generally more in line with professional musician rather than audiophile.
As for why you'd buy CIEMs, its mostly about better isolation and comfort. Your average customs will have a quality on par with universals a bit below their price but will be more ergonomic and isolating. The benefits are generally more in line with professional musician rather than audiophile.