I think all you need is horizon. Thats all I used.
Basically you should make sure the flashdrive is formatted for xbox.
Next, save like some kind of ch2k8 profile or save to the flashdrive while you are on the dashboard. Take the flashdrive out of the xbox and plug it into your pc/laptop. Download the truegameplay roster to your computer harddrive. Open up that horizon program and extract the game save that you copied from your xbox to the flash drive and also drag&drop the roster file you downloaded into horizon.
Now, copy and paste those 3 id numbers from the file that came from your xbox originally into the corresponding spaces for the file you downloaded(like the console id, etc). Now in the downloaded file you should have the copied and pasted information and the true gameplay rosters. click rehash and save and then save the file to device(aka the flash drive).
Go back to the xbox with the flashdrive and now you should be able to copy the true gameplay roster onto your xbox hard drive. You can take the hardrive out, put college hoops in and just load the roster file as you normally would. Hope I wasn't too confusing. Its pretty simple after you do it the first time.
If worst comes to worst go into the 2k13 forum and look for the topic how to rehash and resign. Since I think the files that appear on this site have already been run through the chrome tool, I don't think you have to worry about any of the steps that refer to the chrome tool. Just the horizon stuff. It could literally take you 3-5minutes to get the rosters from computer to your xbox. Once you get the hang of it, you will probably always seek one of the os user created rosters. I mean the level of detail that these guys put in is amazing.