That's the problem - the gain setting on the sub is at it's ABSOLUTE minimum - can't go any lower. And the 990 sub channel is at -15 dB. I simply have no more room to go down. My only option seems to be to increase the levels of the other speakers.

But this seems quite odd to me. I shouldn't have to set the sub's gain to it's minimum and the 990's sub level to it's minimum (-15 dB). Or am I wrong?