to M3 is compering lead to gold.Ah ....
And Mach3 is the gold I presume?

Mind you, I can't help feeling that the Mach3 (UCCNC, LinuxCNC) direction is the way of the future. Proprietary HW/SW combos (such as Fanuc) always lose out to 'Open' SW ime. Yes, it may take the 'Open' SW a little while to get there (budgets, budgets), but just look at every supercomputer and every web server out there. And I find those massive (Fanuc-style) front panels quite boggling compared to the simple GUI of the more modern systems.
I am told that if you want to add a new g-code command or a macro facility to one of the older systems, it can cost you thousands. With the PC versions you usally get everything in the first package, with no extras needed.
I'm raving, and diverting the thread. Sorry. To the best of my knowledge, the ESS does not support backlash correction itself. It would be a silly idea to try imho.
Cheers
Roger