for the wiring of the speakers --------what size gauge are these -------too thin would not be very good for the highs-mids and may lead these in the screeching issue , second thing would to use the 8 ohms terminals and on the preamp , lower the level of the treble controls until the sound is more pleasant ( if there is a tone control ) ----finally , verify the crossover to make sure all screws are tight and replace only the capacitors , with newer ones , ----------there are settings on the crossover , you can lower these by 1 tap -for 3dl less on the tweeter -