What I did was use a line output converter. Just wire it into your rear 6x9's and run your rcas from the converter box. But make sure you get a good quality one like the JL Audio clean sweep or Rockford Fosgate threesixty.1 otherwise at high volume the sub fades out.

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MECA SQ JL AUDIO 500/1, 300/4, 3-10w1v2, XR650-CSI, Kenwood DDX-6019 , Alpine amp and JL TR400CX center channel , 300 lbs of Dynamat.