Aprilaire 500 Install Help

I am installing an Aprilaire 500A whole house humidifier on my Carrier Weathermaker 8000 forced air unit. I have everything installed and I'm ready to do all the wiring. The model 60 control that I got is different than all the ones ive seen before. Instead of 10 screw terminals, this one has 11 with an additional Gf terminal. I could hook it up the way the instructions show, but it seems considerably more complicated than it needs to be. My furnace happens to have the HUM and COM points which should make this a breeze - can I use these instead of the goofy instructions they provide? What terminals get connected?

As a side question, on my furnace I noticed a second 18/2 line coming in and connecting to the Y and COM terminals but I dont know where it goes. It is not the thermostat wire and I have no other controls - could this be going outside to the A/C unit?