Do a search of this forum's archives. This has been discussed before, so the information is out there.
You didn't ask specifically about subwoofer info, but I'll offer some. Myself and others here have commented on how good the quality of the stock audio system is, but that it needs a sub to help out the low end. So, I've been doing some research and have started to build a sub system for my car. What I've found is that AudioMobile subs are a great choice. Their MASS 2012 model is HIGHLY regarded for car audio applications. It has been ranked among the best 12" subs available. Since they sell only direct (no dealers or distributors), their prices are good too. You can see them at
www.audiomobileinc.com.
I'm also building my own sub box to fit tightly into my IS and take up as little room as possible. I'm almost done and am excited to hear the result. By the way, the amp I'm using is a 250W Xtant mono sub amp.
Rob
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2001 IS300
Spectra Blue Mica/Ivory
LS, LD, HH, SR, 17" wheels
2000 Jeep Grand Cherokee Limited
4.7L, QuadraDrive, UpCountry
Patriot Blue, Fully loaded