IMO, Better amps, & speakers don't help with a poor quality radio. My 2002 Santa Fe LX had a crummy radio, a lot like the one in my new Tucson, washed out, airy sounding (especially in the Bass). AM reception is very poor? But, the 6 disc changer, & premium radio in my 2005 Tucson LX was quite good whatever brand it was? I never changed the settings on it, but on the new Tuc I have the Bass set to 10 (the highest) at all times just to get some decent sound out of it.
Of course aftermarket better stereo brands usually have an extended high, & low range, compared to the cheaper brands. You will pick up more highs, & lows, that weren't there before, even when using the same speakers. I found this out yrs ago when shopping for a home stereo, but they all handle Bass differently, some have a lazy, boomy, bass, some have a sharp, tight, bass. Usually those with the lazy, boomy, bass will distort the voice as well, so it doesn't sound normal. This is most noticable when listening to songs that you know, not sounding right? Or listening to a talk radio broadcast.
Bargain Stereo's:
Panasonic, or (Technics) is one of the brightest clearest designs, but may get on your nerves after awhile, Pioneer, & Kenwood, both deliver more highs, & lows, with better separation, and more pronounced bass, both easier on the ears, but the Pioneer has a lazy bass, and the Kenwood has a tighter bass, of these two the Kenwood sounds more natural at all times.
Another factor is the box, is if it's a "Bass reflex" type box "ported" it's (easier to drive), or a tightly sealed box "acoustic suspension" (harder to drive) maybe even with baffles in it, I think it's called an isomeric design? Woofers usually are either bass reflex, or acoustic suspension, Subwoofers are either acoustic suspension, or isometric design delivering the deepest of Bass.