If you just want to hook up subs why not just buy the L7 harness sold by member Technic? I think it's around $100.
2008 E63 M6
- Black Sapphire - Sepang Bronze Full Merino - Carbon Fiber Trim - Alcantera Headliner - SMG - HUD - Soft Close Doors - Comfort Access - Individual Audio w/Sat and HD Radio
2009 E92 335i
- Black Sapphire - Black Dakota - Burl Walnut - Sport - Premium - Cold Weather - Navigation - L7 - Comfort Access - Smoker's Package
Member: BMWCCA #471614