First thing, you should confine your questions regarding the d-league to one post. You have three post covering the same subject.
The D-League mod I'm referring to is made by Jaws2K (or JAWSFreelao). https://sites.google.com/site/jaws2k/home
Maybe you are referring to an older mod but this is the latest D-League mod that I know of. This mod contains all of the necessary files except a readme file explaining how to install the mod.
JSGME should be used to install one mod at a time. It should be used on a plain install (without any mods). It is used to save hardrive space. Otherwise you would have to copy your NBA2K folder and rename it for each mod you want to play. This wastes space by duplicating any files common to all mods. Some people find JSGME too difficult to understand or use but it is actually very easy. You should create a March Madness folder and a D League folder in the MODS folder. Activate one mod and play the game. If you try to enable a second mod, JSGME will give you a warning that the file(s) have already been enabled. For example, a uniform may have the file name UA005.iff. If you try to enable a second mod you will have uniforms mixed in the two mods. This happens because the mod overwrites the original NBA files and both mods have a file named the same.
I think Andrew gave the correct information about the MyCareer issue but you should read the post or ask the question in that post. I know the post is very long. If the forum search does not find the information go the the original post. Press CTRL-F. Type in mycareer. Using the up/down arrows and switching to the next page, you may find the information you seek.