I'm not sure who makes the 6th gen head unit, but the '01 speakers are Pioneer. I find the system to be reasonable. I'm not so sure it'll sound any better with just an amp, I don't think the speakers can really handle too much more power than what the head unit can already pump out. Bear in mind that many factory systems are already tuned, thus changing an element of it could make the system sound much worse.
Now how you like Pioneer is a different matter, but obviously you do.
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