Can't tell by reading the DSP specs if it's a hardware limitation or not. You can change the Q parameter to have it cover a larger spectrum if you need it to.

I also would like to see details of the loudness feature's boost frequencies. My real dream would be to be able to edit the upper cutoff point as well as the loudness boost, so that I can program a perfect-sounding system at 0db with no loudness, then adjust the loudness levels to compensate only for lower-volume playback.

See, as it stands right now, even a maximum 0db volume, there's still some bass boost from the loudness. I'd rather adjust the cutoff so that the loudness disappears completely at about -5db or -10db, and then have it really crank for lower volumes.