M3D sort of simulates surround sound by seperating the reverb from the stereo channels in the front. It should work well for music, but for games and DVDs it should be left disabled. 5.1 sound would require a center speaker which I don't think the Z560s include, so 4 speakers should be the best choice in the Surround Mixer (don't worry about the missing .1 indicating the subwoofer as the bass will be sent to the Z560s just fine). I think 100Hz is usually the best crossover frequency, but I am not sure on this for the Z560s. Hopefully someone else can chime in 🙂