i dont know what the mazdas head unit is but if you go to crutchfield.com you can get everything you need from head unit to amplifier and speakers and they tell you what fits your car. if your gonna change the head unit u will need to get an adapter to connect it, you will find it on crutchfield. as for mix matching, ive never had any problems mix matching audio components, sony has some high end stuff and some reasoably priced stuff as well. but as for amplifiers go you can probably pick up a used one on craigslist or elsewhere online used for a decent price. just make sure you see it working before you buy it. other then that rock on!!!!