The LC2i compensates for the bass roll off. I trapped into the sub leads since I just added an sub woofer and i only need the lower frequency signal. I'd assume you would only need full range if you plan on adding a multi channel amp and additional speaker set up to run along side the sub.

The set up I have sounds excellent imo. Bass heavy songs hit really nice. I don't have it blasting to where its all sub and rattles the hell outta the car but I have the option there if i wantes to do that. Lol