Varaxious

ok it seems that everybody has the same problem that i have with the sub in the back of their car. Does anybody know if there is a company out there that makes a sub that will fit in the space of the current sub without having to do any cutting or welding? if not do you think i should just spend the money to get another sub... oh and one more question is our system digital?? or what ever its call... when it uses fiberoptics... how do you make it work with a speaker that isnt... (uses positive and negative wires)