I pretty much always suggest setting all speakers to Small with a receiver crossover of 80hz. Since the receiver is managing the crossover, put the sub crossover knob on bypass, or turn clockwise to highest setting.
Receivers can differ from brand to brand. Most people that set their mains to large, then put the receiver in LFE+Main mode. This way your mains will be receiving the full frequency as does the sub, it is not bypassed. The sounds from the other speakers will be directed to the sub, based on the crossover setting on the receiver.
