Think something must be wrong, Im afraid. I use 804s - previously with a 558.2 and now with a 559. You are quite right that they come alive at higher volumes. This is a known trait of all nautilus series speakers but particularly the 804 and 803.
However, my normal listening level is on "62." At 80 the sound is verging on deafening. I don`t think Ive ever been higher than 85 but there was no clipping, no distortion - in fact nothing unpleasant could be heard other than my normally tolerant neighbour banging on the partition wall..........

G98, HD621, 568.25, 558.2, 559, B&W 803Ds, HTM2D, 4xSCM1, ASW850, Pioneer PDLX5090 50" Plasma, Cables by Atlas and Chord