Heck yes I'm OK with off topic traffic! Don't make me post another naked picture of Kim Jong Il. hold me back...
EDIT: REMOVED PICTURE OF NAKED KIM JUNG IL... they are liable to take down ecomodder if it was discovered. It's not worth the risk! haha
I could definitely use beta testers. They should be fine, as it's basically the same thing I've tested. But I passed a kidney stone doing like 10000 different variations of component positions and routes so as to make it a good 2 layer layout, with good ground and power planes.
I would use shielded 7 wire cable like this for the interface:
Buy High Quality RS232 extended distance cable to eliminate signal noise and loss of data
The PWM signal should be from something like a pwm channel in a microcontroller, or an AND gate, so that it's actively forced high or low. I've tried it in a few noisy environments like big high frequency switching transformers, and haven't had any problems. Don't use a pull down resistor to cause the pwm to change from high to low (or pull up resistor to go from low to high). Different lengths of wire don't matter much. Propagation delay for current in a wire is on the order of 1 NANO second for each 6 inches of wire. But there is going to be a variation of 10's of nanoseconds from the optocouplers between different FOD8316's.