Iardon,

This could be off in left field, but let me play this out. You said earlier that the "clipping" you're hearing is only happens when somebody is screaming in a movie. Are there any particular scenes in a particular movie that this happens in? If so, does the "clipping" happen everytime this scene is replayed?

I say this for this reason. One is that if you know where to look, maybe somebody else can watch the same movie on their set up and see if they have any "clipping" at the same point. It's truly possible that you're actually hearing distortion from either the microphones used in the scene or it's on the medium the soundtrack was recorded on. Your M&K speakers are known as very revealing and detailed speakers. It's possible you're hearing a mistake in the recording rather than a fault in the equipment.

If you had said that you heard "clipping" during explosions and loud scenes then it might point to the amplifier. But saying it happens when there is screaming makes me question the source.

Just thinking out loud...