I always EQ over Audyssey as I find it gets close but I can do better.
Just apply a 1st order butterworth where you want it to start rolling off after the Audyssey does its thing. The "phase" issue introduced should be unimportant, especially since your interested in decreasing output.
You can see the phase implications by looking at the group delay plot. Anywhere you apply significant eq prob indroduces some GD.
Don't waste time reading signatures.....