@Basicme just checking back on this, it sounds like you were able to create the multi-room group of Echo devices, but they will not all play music at the same time, it only comes through on a single device or maybe on none of them?
You are running in Bridge Mode now for your SSID, and there is no L2 LAN isolation turned on right? That setting is under the Wireless > Firewall and Traffic Shaping page. So if you go to Network-Wide > Clients you are able to see each of the Echo devices in the clients list? They all have an IP address on the same subnet/vlan? And perhaps from some other device on your home network you can ping the IP address of each Echo device?