Go look it up, but the torsen system is a full time system, i.e. torque going to all wheels all the time. it went from a 50 / 50 system to a 60 / 40 rear bias system starting in the mid 2000's on the S and RS. The torsen locks up when it senses slip up to (I believe) 75 percent to the non slipping axle. This system was originally designed for handling in race applications until it was outlawed because it was so good, but was quickly transferred to road going applications because of the traction benefits in slippery condition's.
Haldex (on the any transverse engine install, i.e. A3/S3 and TT) is effectively a fwd car with torque transferred electronically if slip is noted on the fronts. Again, I think it is normally a 95% / 5% front biased system, but can transfer 100% to the rear if conditions warrant.
Bally's, please correct where I went wrong