The old adage is pretty simple...
An audio system is only going to be as good as it's weakest link, and 99.99999% of the time that link is in the install. By install I mean how well the products are installed, are the components placed properly, is the wiring sufficient, how well the system is tuned - all of that. If you're spending a large wad on equipment, you sure as hell had better either front the money and get it installed by a professional, or learn how to do it properly yourself. You can have the best sub in the world, but if you're just going to throw it in a flea market bandpass box, then you're just pissing into the wind.