It should be possible to have din1 be fwd and din2 to be reverse. you will also have to have it set up so that when it sees either command it will run in that direction and if it sees neither command it will be off.
It is then easier to have M03 be fwd and M04 be reverse in mach3.
Since it looks the the breakout board pins are the same as p-port pins numbers thru the smooth stepper hook it up this way.
Pin 1 to din1 = fwd. pin 16 to din2 = rev. using the N.O. contacts.
Then go into ports and pins in mach3 and setup the same thing for pin numbers.
I don't have a computer with Mach3 in front of me or I could give you a more detailed explanation.
If you have the VFD set up with a minimum speed, be aware that when you give an M03 or M04 command the spindle will start turning, even without an "S" comand.
I will go way out on a limb and assume that pins 14 and 8 are for a step and direction spindle, which you are not using. You are however using pin 14 for this setup in a different fashion so you can't use pins 14,16, or 1 in the other places it shows up on the board.
In mach3 it is asking for "outputs" 1-6, not pins 1-6.
Use output 1 for forward and output 2 for reverse. Then under ports and pins in the output section you will set the pins to 1 and 16 for outut 1 and 2. Just make sure that you don't start using the same output for more than 1 funtion, unless you are very sure about what you are doing. You may also have to set active low or high to get it to be on when you want it to be and off when you want it to be.
I believe that you will be generating a pwm signal from mach3 and it will get converted to an analog 0-10v signal on the bob.
Make sure you download a copy of the Mach3 users manual and read it twice. I have gone thru it 3 times now and I am still amazed at what I missed.
Let me know if it helps or I can go more indepth when I am in front of a Mach3 computer