how would replacing the factory amp with a five chanel and of course the speakers but keeping the stock sub enclose and changing out the sub to a JL audio W3

 

That enclosure is designed specifically for the Infinity woofer. Although this hasn't been tried yet to my knowledge, my first guess is that you would get some weird resonance/vibrations, plus there might be some fitment issues too.

But it sounds like you're pretty dead set on doing this, so I would encourage it. Even if it doesn't work out, you can always get another enclosure.

 

that just might work... but like delta said, that enclosure was made for that woofer... it might cause some rattles, but that's all that i can think of...