I think I partly misunderstood what you were saying and thought that you were perceiving the high frequencies as harsh. Getting a “blurry” sound as the volume increases sounds like distortion to me. Though I think it could also be related to the following, which I didn’t explain very well. To much Tequila?
Also many speakers don't have tweeters which can keep up. As the volume level increases their dynamic range compresses. So at different levels the high frequency response is different. With two tweeters the M80s can play much louder without compression.
Thanks for explaining what I was actually trying to say.
When I demoed speakers, besides the outstanding bass, the thing that actually struck me the most about the M80s was exactly what Chris describes. The M80s were the only speaker I demoed who’s highs “kept up” with the mids and lows as the loudness increased. With all the other speakers I heard the mids and lows became dominant as the loudness increased.
