Filling holes is hard. You hit a ceiling after a point and then you'll lose all headroom and bad things happen.
Of course, in theory, I suppose you could turn the levels on the sub way up (such as a doubling it, which I know the 3910 will let you do) so that the lower part of your valleys are near the ideal level and everything else is outrageously loud... then you could cut all that other stuff down.
Don't know if I'd recommend such a couse, or what attendant problems that might bring, though...
