IMHO you're better-off getting a sub & amp seperatly, with a decent wiring kit too
If you think about it, most (almost all) active subs are a money/space/time saver for the user AND the installer.
Cheap & cheerful bass for the "do the job rightly" gang.
main advantages of sub & amp are
build quality (depending on make)
sound quality (depending on make)
choice of install (how it all goes in, most people dont want a big box rolling around the boot
seperate units if one should get "sick or die"

- you can just replace the part you need to, or even upgrade a part of your setup when you want without having to change everything
Trev