Agreed with Wid. Almost always you never want to go higher than 80hz due to localization. With the m80s 60hz is a great starting point. Also try not to overlap the bass from the towers and sub. Sometimes it's good sometimes not. Set the crossovers to blend at same starting position. So 60hz high pass for m80 and 60hz low pass for sub. Play around with settings a bit to see what works best for your setup.