So the deal with brakes is that bigger is NOT necessarily better. You can't slap bigger calipers on and expect better braking... in fact the opposite is most often true. The caliper piston bores are what determine if they are compatible. Obviously the FX brakes are not too small, or you would hear about brake issues. If you did put on calipers that had much bigger piston bores, the balance of the system would be changed (in a bad way) and your master cylinder and brake pedal would no longer work as designed.
The first generation FX can take the Akebono caliper upgrade from the second gen along with rotors - a couple members on here have done it. There are also a few BBK options available, but those calipers are engineered to have the SAME force output as stock, even if they appear twice as big in size. Search on FB groups as well - the Akebono swap is covered there.
