Which version are you using? I believe the issues you are having are addressed by the new data tree structures implemented in the latest versions of GH. In the new versions, components that create multiple outputs for each input they receive, such as split curve, create those outputs in sublists, just as you describe. you can get the latest one from the thread at the link below.
http://groups.google.com/group/grasshopper3d/browse_thread/thread/fc18bfb6795179c8?hl=en# Good luck
