I guess this is the drive board that came with the motor??? i.e. ripped out of the original treadmill???. From what I've seen these driver boards vary a lot, from moderately complex ones that have all the control stuff on board and are fed directly from a pot on the control panel to things like this where it looks like there's no more than the power switching stage and all the clever stuff will be being done with a microcontroller on the treadmill control panel. From the information available I would agree with Doddy, it'll need a PWM signal to feed it, can you get this from the BOB and control vis Mach3 (which I know very little about, but found this which would suggest it's possible, but might need the signal inverting: http://www.audiohms.com/en/blog/item...y-pwm-step-dir).
From looking at other similar circuits I would guess the frequency would need to be between 12 and 25KHz - if you have problems doing this then it would only take a little while and about £1 of components to make a simple analogue circuit that would generate the required signal from the 0-10V O/P. Alternatively you could ditch this driver altogether and go for something like this: https://www.ebay.ie/itm/180V-200V-DC...NVdb:rk:2:pf:0