It seems that the standard boards are limited to the 5 input lines on a LPT port, is it not possible to use these lines as a 5 bit word, that would give us 32 possible inputs (i think) but would need a little change or secondary add-on to the breakout board plus a decoder at the Mach3 end.
Just a thought, the breakout board end id simple as it can be a secondary encoder board connected to the standard input lines, Mach on the other hand I don't know about.