A PCI parallel port card would get you plenty more inputs. There's probably a more elegant way to do it though...
Theoretically 3 inputs is enough if you put the switches in series/parallel etc with each X home switch on separate input - it's a matter of if mach3 can handle it. I'd like to know for my router...

I had a look at giant cod (what an odd sentance!). There's some interesting things but it's still a bit more expensive than www.hobbyking.com. Maybe I could use an E-bike controller on my motor.