I am not sure how much information i can give out so ill try to be sufficiently helpful and vague at the same time.
We are currently using Motionbuilder 7.5 with an A.R.T. Dtrack system with the modtrack plugin to interface between the two. We are keeping 7.5 because the modtrack plugin is not supported through motionbuilder 2012.
ART site http://www.ar-tracking.de/Home.10.0.html
MODTRACK developer site http://www.iais.fraunhofer.de/MotionCapture.html
Is there a plugin that works with the A.R.T. Dtrack system and motionbuilder 2012?