Alex,

I set the 80s to small. On my Denon I have "direct" and "stereo" modes. Direct by-passes all filters while stereo preserves the cross-over and allows you to tweak bass & treble. On direct, the bass is sent to the 80s and the sub regardless of whether the 80s are set to small/large. On stereo, the bass is sent to the sub only. Like others have said, try both ways and see what you like.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated