How do you wire six 4ohm dvc subs to 1ohm?

one of my 15" L7's has a strange rattle sound @ high volumes but only on certain low freq and their still pretty new so dont understand so i was gonna replace the both of them with six 12" hifonic subs , do you think the six 12's(300rms each) will produce more spl than the two 15"L7's?