The LC2i has the ability to split the input signal to send a full range signal to the door speakers, and then send a separate low passed signal to a bass amp.
So, if the LC2i is purchased for powering a sub amp, only the bass output would be used. However, if another amp is purchased for the door speakers down the road, then connect that new amp to the main output of the LC2i.
The bass output has a low pass at about 1 khz and variable output with the ACR-1 remote, whereas the main output is full range with a fixed output.
The AccuBASS® functionality is only present on the bass output.
Click on the wiring diagrams below to enlarge:
LC2i product page