Do you have an SPL meter? How loud was it? If it was above 100 db SPL then you might be "pushing" your speakers too much.
See this article Unreasonably large distortion in midrange drivers. You can see that it gets bad above 105 db SPL.
The main issue in the midrange and tweeter is excursion outside the non-linear range of the driver rather than amplifier power. This is why many studios use horns and why most speakers for sound reinforcement uses horns. The fact is that most normal speakers (even good ones) compress and distort above 100 db SPL (at the listening position - which can be 110 db SPL for the speaker).
See this article Unreasonably large distortion in midrange drivers. You can see that it gets bad above 105 db SPL.
The main issue in the midrange and tweeter is excursion outside the non-linear range of the driver rather than amplifier power. This is why many studios use horns and why most speakers for sound reinforcement uses horns. The fact is that most normal speakers (even good ones) compress and distort above 100 db SPL (at the listening position - which can be 110 db SPL for the speaker).