Rex files are a proprietary audio file format owned by Propellerhead the makers of Reason and Recycle. They have embedded slice markers for timestretching and tempo changes. In some software (Ableton, Maschine are 2 examples) the Rex files load already sliced. But you need Propellerhead's Recycle app to edit the slices manually.
In most Rex compatible apps you can change the project tempo and the Rex files will automatically follow the tempo change. I don't know if that's the case here. This thread said that they loaded in the Ren but had to be sliced manually.
viewtopic.php?f=36&t=160197 Akai bought Sonivox and for years they used a lot of Rex files in their sound packages. Rex files are compressed and smaller than their WAV/AIFF counterpart, but sound basically just as good. They probably left some legacy content in the Rex format to save time and maybe cram more on the discs.
Is this your first MPC? In any case this forum is the most invaluable resource for an MPC user. But you'll have to narrow down your questions to basic keywords to realy find what you will be looking for here. (I just looked up stuff on here for 4 years before I even posted once).
As a new product the Ren/Studio forums are the busiest here lately so you'll find a lot of info and help. If it is your first MPC and you're not accustomed to the Program/Tracks/Song Mode structure of an MPC just watch some basic videos on You Tube. All the MPC's over the years share these basic foundations.
So all I can help you with really is the Rex explanation and assure you that if your questions are more specific there's no shortage of other users who will step up to assist you. Good luck man, it gets way easier once the basic concepts are learned.
