The best way to do 4 outputs is to use 2 DualHead2Go.
You can also use 2 TripleHead2Go if you use the Digital version and simply turn off the 3rd output. This is what I do to get 4 screens so that each output gets identical scan rate and resolution.
This works perfectly for me every time on X1900s.
Granted, you'll have no preview but 4 solid outputs.