Leaving isolated drive for now ( I suspect yours is isolated)
You may be on the button WRT the white box which appears to be a 24v power supply.
I am thinking that this would be needed for your spindle to be controlled by Mach 3 and your Bob.
So test the DC output and report back. If output seems OK then follow it through to the Bob.

I can see some queries with regard to some of the Mach 3 settings I see , but lets go one step at a time !

As an aside I was advised to leave mach 3 and go to linux . Hard going but worthwhile ,
but I would stick with M3 until you see all functions working.