The XA-232 makes it possible to use Mamiya 645 Pro Lenses in combination with the X2-PRO system.
Mamiya 645 Pro lenses can be set manually to the desired aperture setting in the contrary of Mamiya 645 AFd lenses.
The XA-232 can only be used in combination with Canon bayonet based SLR bodies and will not work with Nikon bayonet based SLR bodies.
The use of a Mamiya lens relates to your sensor size as the same focal length in 35mm format, so f.i. a 45mm Mamiya lens will have the same perspective on a 1Ds as a 45mm Canon lens;
for the smaller sensors the maginification factor will apply of course.