Scott is suggesting that you turn the volume down at the LFM-1 Plus's amp - the volume control is located right next to the input jack. I would suggest not going higher than 50% of max, and you could probably do OK with more like 40% - you might simply aim for setting it so that it matches the knob position in this picture . That will allow you to adjust the 990's subwoofer trim up in the channel calibration menu, increasing the signal strength and making it easier for the auto-detect to trigger on.