Dynamic EQ is an Audyssey feature that allows your speakers to sound (for lack of a better word
) more dynamic at lower volume levels. I just bought a Denon 1909 in part because of this feature and the dynamic volume feature, which is an Audyssey feature that keeps dips and peaks in volume levels contained. This feature is really helpful when watching at night and keeps the always annoying volume jump of commercials in check.
http://www.audyssey.com/technology/dynamicEQ.html
http://www.audyssey.com/technology/dynamicvolume.html