The elite trigger is an upgrade as far as I'm aware. Regular models have the exact same trigger pull- I know my PM9 and CM9 do. They are exactly the same.
I have heard nothing about different chamber finish- only the rifling with regard to the barrels. I will have to inspect mine later and see if I notice anything.
Nobody mentioned the MK9 much. I guess people don't think the steel and extra weight adds the value or is worth the extra money
Honestly I haven't ever had the chance to check one out- they're just not that commonly seen in my area; Kahrs in general are not easy to be found in local stores. But they weight would put me off; if I want to carry something that heavy and don't mind something a bit larger I'll just go with a Glock 26.