You should explain which components you have. It's possible that you bought lower efficiency speakers then the ones you had before and to get the same volume you drive the head unit into clipping.Start with Stereo, and yes you are correct the Amp will only Amplify the Sound of the Stereo. But don't let this throw you totally off, a Bad, Cheap Amp has it's own Flaws too. Pioneer is a decent Brand, No complaints that I am aware off.
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