My MR2 turbo also had a similar 'subwoofer' setup behind the drivers seat. I managed to blow that speaker and rather than replace the factory one I bought an 8 inch rockford fosgate sub (not amplified) and box that I wired directly to the wires from the stock sub. This setup worked well in the MR2 and I yanked the box out when i sold the car. I wonder if I can do the same with the 4runner? If those little boxes are amplified, maybe I can unhook one and add a little (better) bass?

Doug

95 Toyota 4Runner V6 auto
94 Chevy Z71
06 Arctic Cat 700 EFI
http://community.webshots.com/user/brownbox