Thanks. Makes sense. As I have not heard any bass dropoff in using only 4.0 and not using the subwoofer channel!The Surround Master does not have low pass/high pass as might be found in mainstream AVR's for speaker management. It's simpler than that. The left & right input is simply summed & sent to a low pass filter & output for the subwoof. If you don't use the SM subwoof output it the level control has no effect on either the main chs or subwoofer output.