I Google'd for this and could not find the answer, then finally found an image with the details on Mazda's Japanese website and thought I'd share in case anyone else is looking for this info:
It's interesting - the 2014 Mazda3 and 6 are mostly identical: 230mm speakers in the front doors, 130mm rear doors, 80mm center channel, and 60mm rear deck speakers. The only difference is the 6 gets a 80mm mid and 25mm tweeter in the left and right dashboard, while the 3 only gets a 60mm full-range in those spots.

It's interesting - the 2014 Mazda3 and 6 are mostly identical: 230mm speakers in the front doors, 130mm rear doors, 80mm center channel, and 60mm rear deck speakers. The only difference is the 6 gets a 80mm mid and 25mm tweeter in the left and right dashboard, while the 3 only gets a 60mm full-range in those spots.