Er6i to a HF5 will be an upgrade in overall sq. I jumped from er6i to er4p and can't imagine going back to the 6i. The hf5 is a bit under the er4p in SQ, but the overall design and cables are better. If you do upgrade, take the time to get adjusted to them.
When I first got the er4p, I was like "these don't sound better". After letting their sound marinate in my brain, I found all kinds differences in sound quality. So, back to the HF5. It'll be what you're looking for. Unfortunately, I can't comment on the ck100, but I can recommend the hf5.