when shutting down my system the speakers squak

Turn your volume level to ZERO before you shut off anything...

>>"no matter how i shut the system down, preamp off first and power amps second or the other way around, i get ungodly squaking sounds from my speakers."<<
>>>>>>>>

You should turn off the power amp first. Turn on the power amp last.

Also when you turn off the power amp no signal should be flowing. By chance do you have a mute switch on your preamp. If so try setting the mute switch to mute then shut off the power amp. See if that helps. You are turning off the power amp with the switch on the power amp aren't you.
Jim

Turn the amp off leave the preamp on all of the time. It uses very little power and will last longer and sound better.

Being as I have remote input selection, I switch to an unused input;then power off. This squak might be tied to using 3 amps---or your line enhancer---or both.

Since the speakers are triamped you must (ought to) have an electronic crossover. This should be powered up and down with the preamp, not the power amps.