I have a few questions about the Fi BTL sub" 1) What is the difference between choosing the options Dual 1 and Dual 2? Ex. Would i have to buy a certain amp if I chose Dual 1 or Dual 2? or if i get 2 subs would i need 1to be dual 1 the other to be 1 dual 2 ? 2) Is there a warranty for the Fi BTL sub, if so how long is the warranty for? Thanks for your time regarding these questions, Alex