What I think you are calling a center dif is the vtd. It is inside an extension housing on output end of the transmission just like the us multiplate clutch awd system. It is operated and lubricated by the transmission fluid, not it's own fluid. I have a jdm driveline in my car. I rebuilt the transmission before installing it and took pictures of the vtd to illustrate what it is. I posted them in a thread detailing the differences of the jdm parts from the US parts:
http://www.subaru-svx.net/forum/showthread.php?t=60414
Your front differential which is mounted on the front of the transmission uses it's own fluid. It will take a little more than 1 and 1/4 quarts/liters of gear oil, preferably the heavy duty hypoid gl5 I posted the link to the information on above.
The rear differential is it's own unit mounted between the rear axles and will take a little less than 1 an 1/4 quarts/liters of gear oil, preferably the heavy duty hypoid gl5 I posted the link to above.