ATTESA/ETS is already complex system, the PRO complicate things more, it's hard to simulate all aspect.
The system can send torque to front wheel when needed, that is when certain condition occur, like when rear wheels speed is higher by 5% than front. Then it works by using G sensors and ABS sensor, monitoring these and adjust the amount of torque at very rapid rate per second.
With the PRO, like fitted on Vspec R34 GTR, can split the torque between each rear wheels as well, not just front and rear. The rear is also fitted with active LSD ( electronically controlled ). This is one of the reason Vspec R34 can drift with rear outside wheel smoking ( gets more torque ) as demonstrated by Dori Dori / Keiichi Tsuchiya in his review on touge roads.
There is also one unique traits of GTR, flat shifting to 2nd from 1st could spin the rear wheels for only split second, making chirping/skidding sound from rear tires as that instant the ATTESA/ETS sends torque to the front. The driver would feel the car jumped like AWD launch
The ATTESA/ETS system diagram / hardware :
View attachment 549381