Hmmm, I gave my "Pre red dot" unit a shot last night. I had a digital source (music file playing on HTPC, PCM format) and set the 950 to "stereo" with the front speakers set to small. The sub was active. Then I set the front speakers to large - the sub went mute (no cone motion at all). Works as it should. Maybe there's something wrong with your specific unit?

Cary