Replaced one stage / major glitch now
Two Matrox Triplehead2go units.
Running 6 stages.
Everything working fine for days.
Then stage 1 (an old unit) starts flickering the images ... so I replace it with identical unit (Christie LX380 projector).
Now stages 1,2, and 3... are all appearing on stage 3.(#1 Matrox)
4,5, and 6 are fine. (#2 Matrox)
Which operating system are you on? Technically, the Matrox site says multiple TH2G unit support is only for Windows, but I have reports of multiples working on Macs too.
You may need to check the output resolution on the matrox. A standard ratio resolution will send one image to the center, and nothin on the sides.
I've used multiple matrox on macs and windows. 2h and 3h2go and there are limitations and combinations that don't work, usually the converter/adapter is the limiting factor.