Do i need a change head unit for better sound quality?

Khanxyz0z

Hey everyone, its my first time buying a sound system for my car, im totally confused, i usually research every topic before doing any mod on a car, but this topic is just so broad

So i went to avenue sound in ny, and he said he would replace my 4 speakers with hertz speakers add an amp and a subwoofer for 1200 plus labor, is that a reasonable price?

And the other question was, since i mounted my ipad mini in the area on top of the head unit, i never use the It(radio) no more , instead i use aux with the ipad so does changing the head unit from stock to something after market make a diffrence in the sound quality? Even though the sound is coming from the ipad from aux,
Do you guys think i should change the head unit at all?
I only want to change it if there is a great diffrence in sound quality

Thanks