I was having trouble with all the rear speakers not working in our 2006 commander, so we installed a new amp and speakers. The navi was working in just the front speakers. Now it is not working at all. installers said that it wont work anymore because we removed the old factory amp..Can anyone help me with this please!!! He said they checked it out and we just cant have sound for navi? IS that true. Does someone know how to hook it back up.