Chris does not recommend 80hz if Audyssey finds your crossover higher as measured "in your room". Do not turn them down.

Large vs Small is determined by your AVR. Denon and newer Onkyo uses 40 hz to make that decision. Older models use 80 hz. Set the mains to small and choose a higher number - 60 to 80 hz.

Dave
Audyssey Setup Guide