The Point is, when you are running any aftermarket speaker(or really any speaker rather), when powering with just the head unit you are not giving the speakers the power they want to see. Just by getting an amp you will improve your system like crazy...even if you dont want to listen to it at higher volumes.
Even some "cheap" alpines or pioneers, you will see a big diff in an amped signal.
Yes that is a 5 1/4th audiobahn mid speaker in my civic's headrest. circa 2006.
2000 Celica GTS
Powerbass 2XL-60.3C 3 way
Dayton Ultimax 15", sealed 4cuft
Memphis 16-MC5.700 5 channel