I thought the speed control was provided by Mach on this machine? Did I misunderstand the thread Ray started on his machine? If Mach controls the speed it must be on. Currently the Mach profile includes control for x, y and z axes so it will lock them, home them, etc. depending on what you tell it to do. It won't free them because it is not in control in that case. Do you create a second profile in Mach so that you can have it control some things, maybe spindle, coolant but remove the control for the x, y and z axes? Would that allow you to crank the handles? What about column elevation (Z)? No handle so you can't move it without Mach. You would be limited to the quill.
As far as using Mach for the DRO in manual mode, won't work. It has stepper motors which do not include encoders to report position. It (Mach) assumes position based on steps taken (not missed steps) that Mach has move them from your set zero point. If it misses steps you are out of position. That is why configuration setup is so critical.
If spindle control is available without Mach then it looks like you have some manual ability dealing with head height. You have a great machine there, I think I would just use some manually entered g code for those times I wanted to make some simple cuts.
Dave