are those some sort of rip off L5s? lol
Well, not to dis the system, I'd say that your smell is the subs about to Voice coils getting too hot, My guess is that what ever song or Songs you play that loud, the sub is playing around tuning freq of the ported enclosure, causing the subs to have minimal movement and overheat. OR you could be clipping the amp sending badly distorted signals to the subs which is just as bad.