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.
2014 Carrera 2S
- White/2 Tone Espresso/Cognac - Aerokit - PSE - PDCC - SPASM - PDK - Sport Chrono - 20" wheels w/OEM Spacers - Glass Roof - Leather Dash - way too much more to list
2013 E92 M3
- LeMans Blue/Black Novillo - Comp Package - MDCT - CW - PP - EPS - CF Roof w/OEM CF Mirrors, Spoiler, Interior Trim - Full IND package - Muffler Delete
2013 F12 M6
- Alpine White/Black Merino - Executive - LEDs - B&O - DA - Lots more