Your first clue is the sound taking a nose dive. Becoming hard, brittle, annoying, listener fatigue, etc. The second clue is any warning LED on your amp. The third is blown fuses. Your amp may not be clipping but may be current starving at some frequencies during slewing, which would cause the "sharp" sounds you are hearing. It is hard to say but you clearly have something going on that is not right. Note that high capacitance speaker cables can also cause this effect. Do you have a long run of speaker cable?
How can I tell if I am overdriving the amp or the speakers?
I have a Hegel H390 driving KEF Reference 5 speakers and when I play something loud, the upper midrange ( saxophone, electric guitar, piano ) start sounding sharp and annoying. The amp is 250 x 2 into 8 ohms, stable down to 2 ohms and the speakers are 90 dbs, 8 ohm, ( min 3.2 ) 50-400 watts. I’m pretty sure it’s not room acoustics, but.
Thanks.
JD