This is right from wetsounds own install guide. Remember the head unit still has a preamplifier, and that is subject to clipping like any other amp is.
http://www.wetsounds.com/media/products ... lation.pdf"2) Turn the radio up to find the maximum volume. Set the system with the head unit volume at 85% of max. This is the loudest the radio should ever go. Radios will create distortion the higher the volume is turned up. Which will create distortion on the output signal before reaching the amps. So find a safe easy to remember volume. If the head unit is 35. Max should be 30. If the head unit is 40."