There is no RCA hookups on the 2006 stock audio unit. You can add a Hi/low convertor to the regular radio harness and then add an amp but it's not as good sound quality. I've done it before and I can't tell but purist think it's a reduction in sound quality. I happen to like the stock look with a hi/low convertor because thiefs seem to pass up my stocker unit.
Here's a quick link that explains them and most any stereo shops have them in stock. I don't know where you live but "Fry's electronics" has them the cheapest near me.
http://www.installer.com/hilo/
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