With overlapping Kinects you have to deal with interference. Here are two interesting articles on how to overcome these problems by using a small vibrating motor:
http://research.microsoft.com/pubs/171706/shake’n’Sense.pdf
http://www.cs.unc.edu/~fuchs/kinect_VR_2012.pdf
Being able to track across the whole range would mean to calibrate the cameras accordingly. You could have a look at some of the projector calibration scenarios – e.g. using a checker board etc.
Heres an article about that with multiple kinects:http://www.graphics.tu-bs.de/media/publications/multikinectsMocap.pdf
I think it should be possible to achieve this also without doing your own tracking, by comparing joint positions and knowing the cameras position / angle.
I think this is interesting too, if you wanna make a joint effort at a multi kinect module i would gladly help.