The smaller wiring harness I believe has all the speaker (-) terminals. While the larger has the powers and speaker (+). I'm not sure what the banana plug you're talking about is, perhaps steering wheel controls? As for ground, I put mine to one of the screws that holds the radio in.
Do you have the inifinity? That might change the ball game. I don't know jack about the factory infinity system.
Do you have the inifinity? That might change the ball game. I don't know jack about the factory infinity system.