I called Marantz technical services and spent an hour on the phone with the tech trying to solve the issue; he concluded that my new sub woofer was defective. So I called the professionals that set up my system and they sent over a tech who changed a setting and all of a sudden the sub woofer works. The 350 page Marantz service manual does not explain what things do in layman's language; and it does not explain how to do things like how to turn on a sub woofer. When you change sources it often has no sound; you have to turn the amp off and back on to get sound. Now the bluetooth app is not working User's recommendation: Avoid this terrible amp; it has serious problems.