I have a JVC KD-SX980 head unit with a JVC CH-X1100 cd charger and four Polk GXR6E speakers. I do not know much about audio components but I would like to add any component to this setup that would improve the sound quality. Any input would be appreciated. Thank you

A subwoofer would help a lot. Nothing huge, just something to fill out the bottom end that gets lost in the road noise.

depending on how nice those speakers are, you could add an amp to power the speakers. Find out the max watts your speakers can handle, and how much RMS they can handle(constant wattage), and find an amp that meets their standards. The amp will put make your speakers sound the way the dealer meant them to. At their peak performance you will get better sound quality at low and high levels and better bass and treble.

You could also add a sub. subs are big, tho and take up space. You could always go for the infinity basslink. It's small and is self powered, so no amp is needed for it. GEts good sound and is very quality.

You need to decide what you want in your system too. Lots of bass for techno or rap that has a nice ringing to it, or bass for punches, or if you're like me, you listen to everything. In this case, you can either get a component system, or a small sub to handle the punches, and get a large sub for the real deep stuff. Or do what i did. I have 2 12'' subs and have one wired for higher level bass and one for deep bass. It's a world of choices. Hope this helps you out.

Amp to power your speakers and a CD you like and some bass.

Thanks for all your replies. The speakers can handle a power range of 2-50 watts RMS and peak power handling of 125 watts. What kind of subwoofer can I get and how can I hook it up to my receiver or can I also connect an amplifier? Thanks

You will need a subwoofer, an enclosure, an amp and all the wiring.

Look for a 10" sub and give it about 150 watts. This will make you happy...for a while...