My mains are in cabinets, yuck,and consequently I have virtually NO room reinforcement in the bass region.

I set my mains to large, which enables me to set my Onkyo 602 "double bass" to "on"

This sends part of the mains lower frequencies to the sub, helping to round out what the mains aren't able to produce in their confining locations.

It takes a bit of a balancing act to get to work right, but it can work very well!

The rest of my speakers are set to "small"