anthrax

I did the brake upgrade front and rear on my 2011 journey yesterday. I used scrapyard calipers from a 2014 and the difference in braking power is very noticeable. The only thing that's bugging me is the brake pedal is now soft. I know very well that this is normal since there is two caliper pistons to move with the same master cylinder. Now, i read that changing the master and booster did not solve this slight anoyance, but is it possible to just change the master cylinder. If they are compatible, the piston size of the new master could offset the pedal softness. I know from experience on motorcycles that it works with the right size master. Did anyone try that, changing only the master cylinder?