well, first off... a properly deisgned bandpass box can do VERY well... get VERY loud and sound VERY good...
the trick is finding one of those... its like the city of atlantis... //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
in short, prefab bandpasses will NEVER sound as good as a properly designed sealed or ported box, will stress the driver severely, and make you look like a ricer (sorry, had to do it...)
Bandpasses are designed for certain drivers, and they will cause a big spike in frequency response at a certain point... if a different driver is put in, it will sound just plain wrong... prefabs are ass... lets leave it at that