Strange AE dilemma

Hi I have a Airport Extreme Base Station connected to the internet via Cable modem. I have an AE connected to my stereo. When I do a reset my home network and the AE show up in my airport. I can surf if I'm connected the the Base Station and I can play music through the stereo if I switch to the AE. My problem is when I try to get the AE to join my existing network after the set up using airport assistant it disappears. I have tried everything soft reset hard reset and same results I'm at a loss as to how to get it to connect to my network. Any help would be greatly appreciated.