depends what car u have i'm gunna assume a u13, if so yes, they came with stock amps
are they front or back splits first of all?
i'd guess front...
i would have a guess they would fit in, can't be too sure as i haven't really looked at my front speakers, but i think the ones that are in already are mounted so ud just shove your new ones in their place
if they are for the back however you would need a mounting kit because 6x9's are already installed in the rear
as for a box thing on your tweeters im not too sure what you're talkin about best bet would just be run the wires that are already connected to the existing tweeters onto your new ones, save alot of hassle unless your thinking of rewiring the whole system and chucking new amps and stuff in,
hope this helps, if you got ne questions feel free to msg
good luck!
*edit* -just checked u do own a u13 so above information should be ok - snailman