Chungvatra

I currently replaced the factory tweeters and door subwoofers on my 2013 gs350 without mark levinson with aftermarket speakers, and I put an aftermarket amplifier on to power those speakers. When I turn on the car the sound came on, but the sound cut off whenever I raised the volume up to 19 and will not come back on unless I restart the car. After checking the voltage I realized the factory amplifier will stop sending signal if I raise the volume above 19. Are there anyone got this problem before? Please advice.