I like the out-and=back plan.
Here is an alternate route for the return trip north from Martinez Canyon:
Of particular interest (to me) is a road not available
to map on google but clearly there. If you look at the satellite zoomed in you can see a road tracing north/northwest from point B to point C. Looks to be a firly tame two-track from the images running a ride and drooping twice or so into canyons (couple of very short wash runs).
That trip back north from Martinez canyon (point C) would run east of the southbound Mineral Mountain Rd/Box Canyon Rd route we did last week on the way in.
Another interesting option is that at point C one could continue to travel up Box Canyon rd (which you've just re-joined) to its terminus (according to the map and (presumably?) rip the wash up to the pint where Yardstick had us on his alternate route last week. Not my thing but the single trackers might dig.