Hi,
the U400 has 34 IOs, and IIRC something like 17 of those are inputs.
If you require 4 inputs per MPG, then three MPGs would require 12 inputs, which doesn't leave many left over
for homes and limits etc.
The ESS has 51 IOs, of which 31 can be inputs, which may give you a bit more scope.
The 57CNC has 57IOs, I don't know the input/output balance but should be enough inputs for multiple MPGs.
The UC300 has 85IOs, of which I believe 31 can be inputs.
I don't know enough about the Hicon Integra but do know that it supports multiple MPGs.
Craig