or do they only fit the non-x models.

I doubt that there are any mounting differences.

thanx

What? No answer. I also wanna get the Akebono BBK on my x sedan. I have the 18" wheel and tire package. Would they akebonos fit without spacers or bigger wheels?

The Akebonos do fit all V36 sedans. As for the wheels, BBK comes with the sedan Sport package and the 18" sport wheels fit over them.

^whs.
To clarify;
The G37S sedan sport 18s fit directly.
The G35S sedan sport 18s require spacers.

yes, but the G37xS's 18" rears are 18x7.5 NOT 18x8.5, So the question is will the rear Akebono's clear?
does anyone know if the rears are smaller than the fronts? if they are they they should since the 18x7.5 clear the fronts.

My guess is, if it's anything like the G35S where the fronts are narrower and have a higher offset, rears wider with a lower offset, then your 7.5's should fit over the rear calipers -- which are indeed smaller. Wheel width is not as much of an issue as the inner barrel and spoke clearance, and offset.

^ +1
Inner barrel & spoke clearance are the issues.
re: the X 18s;
The only way to know for sure is to find someone with Ake & do a test fit.

I thought the xS models have the same size wheel front and rear? If so, then the rims will defintely clear the rear Akebono calipers (per your statement that the rims actually clear the front Akebono calipers) because the rear calipers dosn't protrude outward as much as the fronts.