I have been trying out connecting my Tyros4 main and sub inputs with the qsc Touchmix16.I connect sub 1 for kick drum and sub 2 for bass guitar and left and right outputs for the rest.The result,i did not like it.now i am going back to 2 channels.My friend has the sd1 plus and used the main and sub outputs with great result.he said that way,he can tweak the kick drum and bass individually.But my Tyros4 sounded horrible. Sorry if this topic discuss before.