Wanting to add a JL W7 sub and amp. What is the best way to get a clean amp signal?

 

Take it to a car audio shop that's familiar with MB Burmester. If you're a committed DIY'er, call Crutchfield and ask for tech support.
(P.S. Thanks for spending so much $$ so that the rest of us can enjoy your soundtracks from the comfort of our own vehicles.)