I'm not sure if this is what you are looking for, and it is a bit over simplified, but:

The crossover tells the system at what frequency and below to send bass content from each speaker to the subwoofer, hence “as directed by crossover”. LFE is the low frequency effects track specific to only movies; in a system with a subwoofer, it is sent out of the sub.

It sounds like, based off of your above post, you are looking to set your speakers to small and have the sub run the bass. Make sure to also set the frequency for your crossovers as well. Otherwise, they will default to 80Hz whether that is appropriate or not for your speakers.