You will want to have them send you the track stems from their DAW. Request the stems in wave file format. If you want complete control, make sure the send the files dry with no effects.
Here is a guide I found online that talks about preparing stems for mixing or mastering:
https://www.justmastering.com/article-preparing-stems.php
You will want to consider setting up a DropBox or Yousendit.com account, because the files will be to large to email.
We also encourage you to create a thread about this on the Presonus user forum.
https://forums.presonus.com/viewforum.php?f=108 This will allow for back and forth discussions.