Problem with rex is that until recently, properheads were not licensing out the rex technology. So the only players out at the moment are samplers where you can import the rex but the actual rex manulipulation tools are limited. However… now that they opened the doors and are licensing the format, I think there will be better rex players like the one found in Reason in VST format very soon. .

My current setup has reason running rex's through rewire into SX as standard practice.