If I understand Carl properly, what he's saying is (I think - please confirm) from the first paragraph: that one the centre-tap to one end of the coil is wired into the cabinet - a half-coil configuration. This presents a reduced torque for the machine (obviously by Denford design) - and those motors aren't particularly torquey to begin with. You can work with this for now at least - it was always a choice on this conversion.

But you're still just getting a knocking noise from the stepper under drive?, can you take a photo of the driver, in particular the connectors/wiring AND the DIP switches? I'm curious about your current setting and the microsteps.

If I was in your boat I'd be setting the driver to 2.5A and 8 microsteps to begin with... maybe even just 1 step to keep things simple. I'd be measuring the volts on the supply to the driver, and even swapping out the driver for another just to check that.

If we're ever allowed out I'll offer you a second pair of eyes if that would help - but I can't see that happening any time soon - and I think you'll resolve this a long time before then.

EDIT: One of those DIV268s has a label, something like "Modified" on it - try that one, it's geared to handle fast signals.