Sound tripping at "not loud enough" volumes

NHT speakers are often inefficient. This means that you have to double the power of your current output to get a little louder and then double it again to get still louder.

As far as the amplifier cutting off it is probably going into protection because it is seeing too great of a load. This could be caused by a short. I once had an NHT speaker that would function fine until it reached high volume levels, at which time the amplifier would cut off and go into protect mode. I took the speakers appart only to find that one of the unsheilded wires attached to the woofer cone was very close to the other wire and at high excursions would touch momentarily causing a short. There was a slight discoloration (charring) of the wires at the apparent contact point. All was fixed by bending the wires appart.

This is not neccesarily what is wrong with your speakers but who knows? It may be.

Good luck!

When you say "7 o'clock" do you mean one o'clock or are all your clocks upside down?

I second Bignerd100's analysis. Think your speakers are presenting an abnormally low load (like 1-2 ohms) to amplifier in mid/treble. The amp then runs out of gas & shuts itsef down to avoid "hard" clipping or the speakers have a protection circuit which shuts your speakers down until voice coils can cool off sufficiently to continue.

Speaker mfrs., in general, specify only a nominal ohm load rating, ignoring the minmum load rating which is what the amp sees.

If running multiple sets of speakers at same time, run only one set and/or buy a speaker selector that won't pass an extremely low load like 4 ohms minimum, which most modern amps are capable of.

It could also be that the nature of the mid/high section load has a component of inductive and/or capacitive reactance that is not to the liking of your amplifer and causing it to go into the protection mode.