Dividing A List

Hi all,
I feel like i have been posting a lot but i need this sort of resolved for this afternoon.
I need to take a list of n number of surfaces and divide them based on what level they are at so i can then interpolate a curve through them and have individual curves per level.  I am already doing it with the SubSet list component, however id like to be able to automate this, so i can change values in the future which i will need to do.  Thank you. I've attached the .ghx for more info

-Boris