I don't have any real desire to run the mains full range. I do it sometimes for music listening when the lady is already in bed, but I prefer the subs in the mix most of the time. One question I did have is you said take the measurement separate and make adjustments to see the result, but I would guess I have to play them both at the same time to see what progress I am making no? I have messed with phase and delay on the DCX but it appears at 0degrees in phase and no additional delay that everything blends quite well. With the mains set to small and the XO points at 60 or 80, the response looks pretty darn good to me. I guess it could only really get better having the subs and mains better time aligned, but I would guess it would boost that area a fair amount more if I DID manage to improve on it even more.
So let me run it down:
Solo speaker sweep and keep that curve
Solo Sub sweep and keep that curve
Run both together while messing with the distance settings (for the subs) and see if it brings up the XO area.
I will be doing this in the XO region with the mains on small, but as I stated, that transition already looks pretty good, so if it all falls apart I will just revert back to where I am now which already looks pretty good...