The switch only applies to the 5.1 analog input of the 950 - not the stereo bypass mode - and it only controls whether or not the high-pass filter is enabled (the low-pass filter that steers data to the sub is always active, something that led them to revise the multichannel analog bass management for the 1070 and 970). The 950's stereo bypass sends full range to the mains, but if the mains are set to small it takes a copy of that signal and uses that to generate a subwoofer signal.