Amp and Car Speakers

I have tried to do a few searches or google and other places. I just cant seem to find the right answer.

I wanted to upgrade my audio in my RSX. It had a bose system so I decided to change everything and put a new amp in the car too. So I picked up a JVC kd-r530 from a friend that wasnt being used. Replaced my speakers with Pioneer 4- way speakers. but the sound was pretty low, so i also installed a kicker cx300.4 amp. Now i have a loud sound, but the bass is not hitting right. i am not getting the bass that i am used to it.

Someone told me that the amp will only help the speaker get lounder and get better sound out of it but wont give me bass. i have played with the eq setting, but not gettting much out of it. plus the headunit does not have a subwoofer on or off option.

Any way i can still get some bass out of it or would i have to get a sub to make it sound better?

thanks