Thanks for the roster file!
I got this information from a YouTube video (not sure if links to it are allowed on the forum):
A program called PS2 Save Builder allows you to extract specific pieces out of a PS2 MAX file. One of the files appears to be exactly the same as the XBOX's DAT files (just named differently). The video shows how to convert an XBOX file to a PS2 one, and I tried to reverse the process. I didn't get any errors, so the attached file might work.
I won't have access to my XBOX until sometime next week to test this on the hardware, but the file does open up as the correct roster in Finn's editor. I hope that this helps!