I wish I had a 990 to put on the test bench to sort things out, but unfortunately I don't. I wasn't aware that the 990 uses white noise - that doesn't make a whole lot of sense from a design point of view - oh well.....

I always recommend TrueRTA, upgraded to at least the 1/3rd octave level, as a very accurate way to analyze the true nitty-gritty of what's going on with a sound system. The new RadioShack meter has a line out jack which allows use of it's mic, without the bass rolloff, for analysis. Seeing the entire audio spectrum at once allows very accurate fine tuning in positioning of the subwoofer, in addition to the mains and surrounds.

TrueRTA Website