I went in originally and selected work offset 3 by clicking in the box and typing 3, <enter>. I then zeroed x and y. When I run the program, while G56 is active, I change an axis dimension (lets say I re-zero x, which is off .001"). When I close Mach3, it prompts me to save the work offset (fixture save?) which I do. I boot up the PC the next day, fire up the mill, do a ref all, and run the program, which drops it in the center of my test fixture (occasionally off by .0005", but pretty good IMHO). If the work offsets are not in the xml file, I can tell you they are stored somewhere. Isn't entering work offset 3 the same as G56?
Joe