set speakers large or small?

set front to large-powerpoints and center to small

Your main speakers roll off at around 50hz, if you set them to large just where you gonna make up those missing 30hz?.....thats a huge gap in sound. You set all to small, roll off mains at 60, center at 60 rears at 80hz and set your sub to cut off at 80hz.........thats the proper way to do it. Why would anyone tell a speaker that rolls off that high that it is "large"?

If you set the front LCR high-pass at 60 Hz and the sub low-pass at 80 Hz you can expect an overlap region. It's not obvious why you wouldn't just high-pass the LCR and surrounds at 80 Hz as recommended by THX. If the processor has a large-small designation, chances are 80 Hz is the cross-over it's using.

db

Set all to small. Crossover at 100, twice the low end of the mains. If you set the x/o lower, you will have a dip in the response because the speakers roll-off overlaps with the x/o roll-off. The 'double' roll-off won't sum together correctly with the sub's x/o causing a dip in the response between the mains and sub. (Setting to large will stress the speakers. They're not designed for handling very low frequencies.)