The problem is that these systems run at a 2 ohm impedance, so any speakers other than OE are poorly suited. As to the front speaker with 2 sets of leads, that front left speaker has a dual voice coil, the second being used for the cellular phone.

The front door speakers are indeed in a box; actually, it's a ported enclosure. I adapted 6" drivers to fit into these enclosures.

Sorry I can't offer better advice, but this same predicament pushed me into replacing my entire system. Good luck!

__________________
"If God had meant for us to walk, why did he give us feet that fit car pedals?" Sir Sterling Moss

Michael
2014 E63S Estate
2006 SLK55
1995 E500
1986 Porsche 944 turbo