.. the distance you stand from the screen being stationary and constant each time you play?
I'm sure IR guns will be especially susceptible to movement towards and farther from the screen effecting accuracy and sensitivity....
It seems that if someone were to make a eight-emitter IR system (four-sides plus the four corners for a total of 8 IR emitters ) that you would not need to calibrate the system after the initial setup (stand x feet away and point the gun at the center).
The firmware could be made to measure the distance from the individually distinct emitters it can see and better infer where the gun is pointed.
Ie. I see the left lower corner strip only, it's width is 200 pixels, I see no other emitters, and I see it in the middle of the camera, so the gun must be 6 inches away, pointed 2 inches from the left because I can't see the bottom middle IR strip yet, and 1 inch above the bottom, because otherwise I would see the left middle IR strip given the width of the corner strip I can see.

A four sided system might work, but the more emitters, the more accurate it can be.
I have no idea how much of what an AimTrak does is on-chip, and how much is programming, but if it is programming, maybe the current sensors could be reprogrammed to work with this type of setup, that way we only need to buy more IR emitters.