John
I felt like I hit the limit with my 60's about a week ago. as in your situation it seemed to have nothing to do with bass. It sounded like the voices got very harsh and there was a mid frequency "clacking" sound. I don't know any better way to explain it. I lowered the volume immediately. Keep in mind this was louder than I would usually listen.

This is in "stereo only" no sub or speaker settings. My amp has a rotary dial it was set to about 1:00 or between 1:00 and 2:00. When I back off to straight up 12:00 it is loud and clean. It is an older HK 150watt rms per. The room size is 15 x 20, 2story, open to other areas on 2 sides. I can't remember what music I was playing.(unfortunately) I have not been able to repeat it since although I have not really tried that hard. I will try more testing this weekend. The weird thing in my situation was I am sure I had the amp at this volume when the speakers were in a smaller room and this did not happen at all. I would like to get to the bottom of this before my 30 days are up.
oz


"Life is what happens while your busy making other plans" John Lennon