You may want to switch it back to "on" -- the low-pass crossover that sends material below 80Hz from the full-range channels to the sub is always active, even when the high-pass crossovers (which are controlled by the on/off switch) are disabled, which is creating the double bass that you are encountering. (Also, for a summary of the 950's bass management options, you might look here . It can get a bit confusing at times.)

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