Golden Dragon:
Ryd gave you some pretty good advice. The reality is that the-all-in-one sub/amp systems will never sound as good as a seperate sub-woofer in a tight inclosure (of adequete size) with clean, high quality power running it.
Now, if you're someone who is not that discriminating, the-all-in-one you've mentioned will probobly do it for you, but for me I would never spend the money on somthing like that.
If clean, simple install, and great sound quality is what your willing to spend your money on I can not recommend anything higher than the JL audio Stealth Box.
http://www.jlaudio.com/stealthbox/4runner.html

They are a fiberglass enclosure desinged to fit seamlessly into the 4Runner and sound great. You'll need an external amplifier and a qualified shop to run power to the amp, RCAs from the head unit to the amp and speaker wire from the amp to the JL box.
This set up with your new polk audi mids will satisfy even the most discriminating listener and with your new head unit you will have the ability "fade" the stealth box for better tunability.

<small>[ March 01, 2003, 05:21 PM: Message edited by: 4TunaRunner ]</small>